Preheat oven to 350 degrees F. Lightly butter an 8-by-4-inch loaf pan; press and 8-inch wide strip of parchment paper into bottom of pan so it lines the bottom and long edges, leaving two overhangs on either side.

In a bowl, whisk together flour, baking soda, spices, and salt.

In another bowl, whisk together pumpkin, sugar, eggs, egg yolk, 3 tablespoons of milk, oil and vanilla until evenly incorporated.

Add pumpkin mixture and melted butter to dry ingredients, and mix until just incorporated and no dry ingredients remain.

Separate batter into two bowls. Add cocoa powder and remaining 1 tablespoon milk to one bowl and stir until just combined.

Use a medium cookie scoop or spoon to scoop batter into prepared pan, alternating dollops of the pumpkin and the chocolate batter in a checkerboard pattern, layering alternate scoops on top of one another about 3 or 4 levels deep. Use a large skewer and swirl the batter, with the skewer touching the bottom of the pan and moving in loose swirling motion to swirl the batter throughout the entire thickness of the loaf.

Bake for 55 to 65 minutes or until a toothpick inserted in the deepest part of the bread comes out with moist crumbs attached (but no gooey batter). If using a 9-by-5-inch pan, the cook time will be slightly less.

Place pan on a wire rack to allow bread to cool completely, 1 to 2 hours. Use the parchment overhang as handles to gently lift the loaf out of the pan. If it is still warm, let it cool completely on a wire rack before slicing and serving. Store in an airtight container for up to 1 week.