1 cup all-purpose unbleached flour
1 cup white whole wheat flour
1 tsp baking powder
1 tsp baking soda
1/4 tsp kosher salt
1 stick unsalted butter, softened
1 cup granulated sugar
2 Tbsp cocoa powder
2 Tbsp instant espresso powder
2 large eggs
1 tsp pure vanilla extract
1 cup sour cream
Baking spray (something like Baker's Joy, or PAM with flour)
2 Tbsp confectioners sugar
Preheat oven to 350°F.
In a mixing bowl, stir together the flours, baking powder, baking soda and salt.
In a small glass measuring cup, combine the cocoa powder and espresso with 2-1/2 tablespoons of hot water. Stir to dissolve, and set aside.
In the work bowl of a Kitchenaid-type stand mixer, cream together the butter and sugar, until light and fluffy. Add the eggs, one at a time, and then the vanilla.
Add to the egg mixture, alternating, the dry ingredients and sour cream. When the batter is combined, pour in the cocoa-espresso mixture, and stir to incorporate it throughout the batter.
Spray a small (5- or 6-cup) Bundt pan with baking spray. Transfer the batter to the pan, and use a rubber spatula to distribute it as evenly as you can; the batter will be quite thick, so it won't be perfectly smooth.
Bake at 350F for 45 minutes, or until a tester comes out clean.
Set the pan on a wire rack to cool for 15 minutes, then invert the pan and remove the cake. Let it cool completely on the wire rack. When the cake is cooled, sift the confectioners sugar through a fine-mesh strainer directly onto the cake.
Note: You can cool and freeze this cake, but if you do, don't top with the confectioners sugar until you are ready to serve.