Preheat oven to 350 degrees F. Butter an 8-by-8-inch square baking pan; line with parchment paper and lightly butter parchment.

To make topping, melt butter in a microwave safe bowl. Mix in sugar until evenly moistened. Add flour, espresso powder, cinnamon and salt and mix until dough comes together (it will be on the crumbly side, but should hold together when squished). Set aside and let cool.

In a mixing bowl or the bowl of a stand mixer fitted with the paddle attachment, cream butter and sugar together until fluffy, 2 to 3 minutes. Add egg and mix until incorporated. Mix in vanilla extract.

Mix baking soda in with sour cream; whisk baking powder and salt in with flour.

Add half of dry ingredients to batter, followed by half of sour cream, mixing well after each addition. Scrape down the sides of the bowl, then repeat with remaining flour and sour cream until just incorporated.

Spread batter into prepared pan. Crumble topping on top, starting around the outside edges and working your way towards the center until the entire top is covered.

Bake for about 30 to 35 minutes or until a toothpick inserted near the center comes out with a few moist crumbs attached.

Place pan on a wire rack to cool completely while you prepare the glaze.

For glaze, sift powdered sugar into a bowl. Add espresso and whisk until glaze is smooth. It should be thick but still drizzle-able, if necessary, add more powdered sugar to thicken it up or if it's too thick, and more espresso, 1/2 teaspoon at a time, until desired consistency is acheived.

Use a whisk or a fork to drizzle glaze over top of cooled cake. Let glaze set for 15 minutes before cutting into squares and serving.

Cake will keep, covered in an airtight container, for up to 3 days.