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Sweet Potato Layer Cake with Molasses Buttercream

Sweet Potato Cake with Molasses Buttercream

I’ve has this vision of molasses buttercream floating around my head ever since Heather came to town. She brought some delightful espresso macarons to her book signing this past summer, filled with a surprising molasses buttercream.

I haven’t forgotten it.

Sweet Potato Cake with Molasses Buttercream

I first attempted to re-work the bourbon layer cake, intending to use it as a base for this inspired buttercream, and also playing with the recipe as it has never completely satisfied me in terms of consistency. Unfortunately, my modifications, which I thought would help make the cake lighter and fluffier, only made things worse.

With another cake failure settled into the garbage and me not wanting to give up just yet, I still needed a vehicle for my molasses buttercream. So I turned to my faithful stand-by: Sky High: Irresistible Triple-Layer Cakes. In it was a recipe for a delightful sweet potato cake. Seeing as how we’ve been getting a steady 2 pounds of sweet potatoes each week with our CSA and a whopping 10 pounds this past week, I had no shortage of sweet potatoes. It seemed it was meant to be.

Sweet Potato Cake with Molasses Buttercream

While it isn’t the simplest cake to prepare, the extra step of whipping and folding in the egg whites make the cake light, with a delicate crumb that most sweet potato or pumpkin cakes lack. In fact, I may have to try this trick on the aforementioned bourbon cake as it could definitely use some lightening up.

The cake itself has a very light sweet potato flavor and subtle spiced undertones. It’s like a milder version of pumpkin pie, only with sweet potato, and cake instead of custard (ok, so maybe it’s not like pumpkin pie at all). But my intuition that it would be delightful in combination with a sweet and sticky molasses buttercream? Spot on.

Sweet Potato Cake with Molasses Buttercream

I’ve slowly realized, over the years of making cakes and cupcakes, that buttercream has distinct seasons (and I’m talking about straight up American buttercream here, don’t even get me started on the meringues and other varieties). Summer means soupy buttercream, so you better have some shortening handy. Spring and fall are ideal for buttercream-preparation, where the temperature of “room-temperature” is, apparently, perfect. But I never thought I’d have trouble with winter buttercream, even more so than the pesky summer stuff. It definitely requires some more experimentation on my part to figure it out, but I assume that the butter is simply too cold. Even at room temperature it’s still a chilly 65 degrees. My winter buttercream often stays thick, bordering on buttery/greasy in texture (even though the powdered sugar makes it plenty sweet). Adding more milk/cream to lighten it up only works to a certain extent, after which adding more doesn’t change things one bit. Poor, sad, moody buttercream.

Guess you can add American buttercream to the ever-growing list of seemingly-simple things with which I constantly battle (including, but not limited to: chocolate, chocolate ganache, chocolate candy coating, caramel, and pie crust).

Perfectly fluffy or not, luckily, it still makes for a fantastic cake.

Sweet Potato Layer Cake with Molasses Buttercream

Yield: 1 9-inch layer cake (halve for a 6-inch cake)

Cook Time: 1 hour

Total Time: 3 hours

Ingredients:

For Cake:
2 large sweet potatoes (about 1 lb)
3 cups cake flour
3 teaspoons baking powder
1 1/2 teaspoons cinnamon
3/4 teaspoon grated nutmeg
1/4 teaspoon ground cloves
1/2 teaspoon salt
5 eggs, separated
2 1/4 cups granulated sugar, divided
1 stick plus 2 tablespoons unsalted butter, room temperature
1 1/2 teaspoons vanilla
1 1/4 cups whole milk

For Frosting:
2 cups (4 sticks) unsalted butter, room temperature
4 cups powdered sugar, sifted
1/4 cup molasses
1/4 cup milk or cream, more or less as needed

Directions:

Preheat oven to 400 degrees F. Prick sweet potatoes in a few spots with a fork, then place on a foil-lined baking sheet and bake for about 1 hour, or until the potatoes are very soft and beginning to caramelize. Remove from oven cool slightly.

Reduce the oven temperature to 350 degrees F. Butter the bottoms and sides of three 9-inch round cake pans. Line with parchment paper; butter parchment.

When the sweet potatoes are cool enough to handle, peel of the skins and remove any blemishes. Pulse in a food processor until smooth. Measure out 1 cup of puree (discard or reserve the rest for another use).

In a bowl, sift together flour, baking powder, cinnamon, nutmeg, cloves, and salt. Set aside.

In a large metal mixing bowl or the bowl of a stand mixer fitted with the whisk attachment, beat egg whites on medium speed until frothy. Gradually beat in /4 cup of sugar, increase speed to high, and beat until the egg whites form moderately stiff peaks.

In another large mixing bowl, combine sweet potato, butter, vanilla, and remaining 2 cups sugar. Beat on medium-high speed until light and fluffy, about 2 to 3 minutes. Add the egg yolks, one at a time, mixing well after each addition. With the mixer on low speed, add 1/3 of the dry ingredients, followed by 1/2 of the milk. Repeat with another 1/3 dry ingredients, remaining milk, and finally remaining dry ingredients, mixing until just incorporated.

Using a large rubber spatula, fold 1/4 of egg whites into the batter to lighten it. Add the remaining egg white and continue to fold just until incorporated; be sure not to overmix the batter.

Divide batter among prepared cake pans and bake for 25 to 30 minutes or until a toothpick inserted near the center comes out clean. Let cool for 10 minutes, then turn out onto wire racks and cool completely, at least 1 hour.

To prepare frosting, in a large mixing bowl, beat butter on medium-high speed until smooth and fluffy, 2 to 3 minutes. Add powdered sugar, 1/2 cup at a time, mixing well after each addition. Add molasses and beat until incorporated. Depending on the temperature and consistency of your frosting at this point, add milk or cream, 1 tablespoon at a time as needed, then continue beating until frosting is light and fluffy.

To assemble, level each cake layer by cutting of the domed top with a long serrated knife. Place one layer, flat side down, on a cake stand or serving platter. Spread on a layer of buttercream using an offset spatula. Position second layer on top and press to adhere. Repeat with another layer of buttercream, and then position final cake layer, flat side up.

Cover the entire cake with a thin layer of buttercream. This "crumb coat" will make frosting the cake easier. Refrigerate for about 15 minutes to allow this crumb coat to set.

Remove cake from refrigerator and frost with remaining buttercream, reserving some for piping decorative details if desired.

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55 CommentsLeave a Comment →

  1. 1
    Posted On November 19, 2012 at 9:30 am

    Hi. Just wanted to say that the top picture? So good it kills me. So good.

    Reply

  2. 2
    Posted On November 19, 2012 at 9:42 am

    This look A-M-A-Z-I-N-G! I’m really curious to know how it tastes.
    And, by the way, the top picture could be the cover of a cookbook: it’s fantastic!

    Reply

    • KaylaR
      Posted On January 7, 2013 at 3:38 pm

      I agree! I am so impressed with how straight the cake layes AND the icing layers are!

  3. 3
    Posted On November 19, 2012 at 9:51 am

    Sweet potato is cake? I’m sold when it’s topped with that buttercream!

    Reply

  4. 4
    Posted On November 19, 2012 at 10:01 am

    Wow! This sounds so interesting! I never would have thought to put sweet potato in a cake!

    Reply

  5. 5
    Posted On November 19, 2012 at 10:04 am

    The pictures in this post are just stunning, like take your breath away stunning. And that molasses buttercream may be what I’m dreaming about tonight!

    Reply

  6. 6
    Posted On November 19, 2012 at 10:16 am

    This looks so amazing!! You should definitely start selling these if you don’t already.

    Reply

  7. 7
    Posted On November 19, 2012 at 10:24 am

    Gorgeous! What a beautiful cake!! I love that you used sweet potatoes!

    Reply

  8. 8
    Posted On November 19, 2012 at 10:29 am

    What a stunning cake and so perfect for the holiday season. I love the cover photo – breathtaking!

    Reply

  9. 9
    Posted On November 19, 2012 at 10:39 am

    Absolutely gorgeous! I can only imagine how this tastes… my mouth is beginning to water. Just beautiful!

    Reply

  10. 10
    Posted On November 19, 2012 at 11:26 am

    Molasses buttercream!? Amazing idea. I was planning on making a sweet potato cake with maple cream cheese frosting but now I am torn.

    Reply

  11. 11
    Posted On November 19, 2012 at 11:35 am

    This cake looks seriously perfect!

    Reply

  12. 12
    Posted On November 19, 2012 at 11:44 am

    Freakin’ gorgeous.

    Reply

  13. 13
    Posted On November 19, 2012 at 11:46 am

    WOW, you take the most amazing photos… that cake looks phenomenal! What are those sprinkles/ decorations made out of, chocolate?

    Reply

  14. 14
    Posted On November 19, 2012 at 12:21 pm

    THIS MADE ME GO TO THE KITCHEN AND GRAB A KINDER SURPRISE EGG BECAUSE I NEEDED SUGAR NOW! :D Wow, what a cake!

    Reply

  15. 15
    Posted On November 19, 2012 at 12:44 pm

    This sounds so delicious! I just love the idea of molasses buttercream.

    Reply

  16. 16
    Posted On November 19, 2012 at 12:54 pm

    This is just sinful…and amazing and exciting and delightful and I can’t wait to try it!

    Reply

  17. 17
    Posted On November 19, 2012 at 1:22 pm

    I was sold as soon as you mentioned molasses buttercream! I LOVE molasses in the fall. It is safe to say that I add it to most breads et al. (at least in a tiny dosis!)

    Reply

  18. 18
    Nichole
    Posted On November 19, 2012 at 2:41 pm

    Looks amazing! Could you substiture rice or almond flour for the cake flour?

    Reply

  19. 19
    Posted On November 19, 2012 at 2:49 pm

    This cake sounds so different and amazing! I don’t think I’ve ever used molasses in a frosting of any kind (I say, as though I’m making cakes right and left–I’m totally a twice-a-year cake baker), and it sounds perfect with sweet potato cake!

    Reply

  20. 20
    Posted On November 19, 2012 at 4:39 pm

    It looks amazing. I’d like to eat it now. :)

    Reply

  21. 21
    Posted On November 19, 2012 at 7:30 pm

    OMG, I don’t even know what to say besides slice me up a piece now.

    Reply

  22. 22
    Posted On November 19, 2012 at 7:41 pm

    Sweet potatoes in the cake!? LOVE this! It looks beautiful – so light and soft – I finally found sweet potatoes where I live and have been excited to put them in everything. This is next on the list – amazing.

    Reply

  23. 23
    Posted On November 19, 2012 at 9:31 pm

    Taking a bath in molasses buttercream is totally acceptable, right?

    Reply

  24. 24
    Posted On November 19, 2012 at 11:30 pm

    I love the flavors you have combined for this cake, and the photo is out of this world. Kinda wish I had a slice of that right now.

    Reply

  25. 25
    Posted On November 19, 2012 at 11:57 pm

    This cake is awesome!! I’m drooling, it must taste amazing, that molasses buttercream is calling my name…Thanks for sharing the recipe…have a great day!! :)

    Reply

  26. 26
    Posted On November 20, 2012 at 3:58 am

    I dont even know where to begin!! The sweet potato cake itself, it looks so moist and rich and fab.

    Then I LOVE molasses and I love….frosting! I don’t need cake, I could just have frosting and this is frosting I want!

    Pinned!!!

    Reply

  27. 27
    Posted On November 20, 2012 at 11:00 am

    This is look F***ING AMAZING.

    I really don’t know how else to say this. I love molasses. My new breakfast is “gingerbread oatmeal” with molasses mixed in. This cake looks so good, my sister who does a gluten-free baking blog (http://cakesnbakes.wordpress.com/) just told me she is thinking of doing a GF conversion on this recipe.

    P.S. — Love that you are fellow designers, this blog is fantastic.

    Reply

    • Posted On November 20, 2012 at 11:01 am

      •This looks

  28. 28
    Posted On November 20, 2012 at 1:19 pm

    I was expecting the cake to look dense and darker in color, but it looks so light. I bet it is such a great compliment to the buttercream.

    Reply

  29. 29
    Posted On November 20, 2012 at 1:20 pm

    That is one gorgeous cake! I love the way you frosted it, too. The flavors sound perfect together. Whoa, that is a lot of sweet potatoes!

    Reply

  30. 30
    Posted On November 20, 2012 at 7:12 pm

    This cake is absolutely gorgeous! I love how light and fluffy it looks, as these types of cakes tend to be dense. Love, love, love!

    Reply

  31. 31
    Posted On November 20, 2012 at 8:04 pm

    Your pictures are absolutely incredible!!

    Reply

  32. 32
    Posted On November 21, 2012 at 2:02 am

    This just looks divine and very decadent but everyone needs a little decadent in their lives. xx

    Reply

  33. 33
    Posted On November 21, 2012 at 11:16 am

    Not only a gorgeous cake, but absolutely perfect for the season! I LOVE your blog!

    Roz

    Reply

  34. 34
    Posted On November 21, 2012 at 1:11 pm

    What an amazing idea and layer cake! Great job on the layers, evenness, and beautiful butter cream.

    Reply

  35. 35
    Posted On November 21, 2012 at 1:22 pm

    I’m obsessed with new and unique ways to use Sweet Potatoes and this definitely fits the bill!

    I recently made a Honey & Gorgonzola Sweet Potato Casserole for an early Thanksgiving dinner.. I’ve got a few spuds leftover and might just use them for this :) xx

    Reply

  36. 36
    Posted On November 21, 2012 at 5:06 pm

    This looks great, especially with the molasses buttercream frosting. Yum. I will have to try it at a holiday party sometime soon!

    Reply

  37. 37
    Phoebe
    Posted On November 21, 2012 at 10:48 pm

    That looks super delicious anything with sweet potatoes would be good!

    Reply

  38. 38
    Posted On November 23, 2012 at 4:06 pm

    yum, this looks great :) I like the idea of sweet potato cake with molasses buttercream. Delicious combo!

    Reply

  39. 39
    Posted On November 28, 2012 at 5:03 pm

    Beyond stunning & gorgeous.

    PS. Nice plate. ;)

    Reply

  40. 40
    Rachel Joy
    Posted On December 2, 2012 at 10:18 pm

    Thanks for the wonderful recipe. Just made this cake for a potluck and everyone loved it! I used the original recipe without the amount for vanilla listed but 1 tsp seemed to do fine. Definitely recommend using the butter at room temperature. Tip: I baked the sweet potato the day before and saved the puree in the fridge for the next day. Still took me over 3 hours but it tasted amazing!

    Reply

  41. 41
    Peggy
    Posted On December 13, 2012 at 2:06 pm

    My sister and i made this cake and it was fantastic!! the cake tastes like pumpkin and the buttecream icing was delicious.

    Reply

  42. 42
    Holley
    Posted On January 19, 2013 at 11:45 pm

    Im in love! This cake was so moist and wonderful! I doubled the amount of molasses in the buttercream. I love molasses and I have a cold, so Im pretty sure that my tastes buds are off, but It worked out and made a wonderful frosting.

    Reply

  43. 43
    Josephene Kealey
    Posted On March 30, 2013 at 7:59 pm

    I made this cake, for my birthday, to share with our little family and our neighbours. It was very very good. Thank you for the recipe. I just finished making the lemon chocolate cake, for our children’s Easter Sunday breakfast (yup). I hope it gets the thumbs up!

    Reply

  44. 44
    Posted On April 23, 2013 at 8:53 am

    This is the first cake I made not from a mix and first buttercream I made! Turned out great and my husband loves it, So glad I found it, thanks for putting it up!

    Reply

  45. 45
    Posted On October 9, 2013 at 6:41 pm

    I came across this on Pinterest today, and just wanted to pop in and let you know that this recipe sounds incredible! The flavor combination is so fitting for this time of year, and a welcome change from the typical apple and pumpkin varieties.

    Reply

  46. 46
    Susan
    Posted On October 29, 2013 at 2:00 am

    I made this cake yesterday, and I think it’s my new favorite cake! Distinct flavors, moist, and sweet without being overbearingly sweet. I’m new to making from-scratch cake, so it took me a long time, but it came out perfect. That being said, I would wait until you have the rest of the batter ready before fluffing up the egg whites. Mine were just starting to recombine into liquid whites by the time I incorporated them into the batter. Also, I didn’t need any extra milk/cream in my frosting. Fall really is the best season for buttercream! Thanks for the recipe!

    Reply

  47. 47
    Liz
    Posted On November 25, 2013 at 1:44 am

    HeyLindsay, is it sweet potatoes (the tuber w white insides but sweet tasting) or is it yams (the tuber w orange insides)? I know yams and sweet potatoes are usually used synonymously but I don’t want to get it wrong. :-P Thanks!!!

    Reply

    • Posted On November 25, 2013 at 9:08 am

      Orange ones. :) You can also use canned puree.

  48. 48
    Patti
    Posted On December 1, 2013 at 3:11 pm

    Did you bake two recipes of the cake?  I’m noticing you have 3 even layers.  At first, I thought you cut the two in half but, when I went back to see the picture, there are only 3 layers, not 4.  Please clarify.  Thanks!  

    Reply

    • Posted On December 1, 2013 at 3:27 pm

      Just divide the batter among 3 cake pans. :) Easier than baking the cakes and trying to split them later.

  49. 49
    Bill Terrance
    Posted On December 2, 2013 at 1:10 am

    I made this for Thanksgiving. It went over phenomenally! That Sky High book is the greatest, your frosting recipe was grand! Cheers!

    Reply

  50. 50
    Sarah
    Posted On June 16, 2014 at 12:19 pm

    I baked this cake yesterday in preparation for a colleague’s retirement party today. It was a knock-out and nearly every slice was gobbled down happily, with a glutinous pride! I found your recipe via Pinterest several months ago and only ventured down the path of making it for the first time yesterday. I will surely return to this recipe again and again. What an excellent suggestion for molasses butter cream. It was the perfect pairing with this cake. THANK YOU!

    Reply

  51. 51
    Arlene
    Posted On October 19, 2014 at 7:10 pm

    Do you think substituting boiled apple cider would work in place of the molasses?

    Reply

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