Preheat oven to 350˚F.

Grease and flour two 9-inch loaf pans. In a medium bowl, combine the flour, cocoa powder, baking soda, salt and espresso powder. Reserve.

In a large mixing bowl, combine butter and 2½ cups sugar. Beat until combined and creamy. Add the eggs, one at a time, beating well after each addition. Add the vanilla extract and combine. On low speed, add the flour mixture, alternating in thirds with the sour cream. Add the boiling water and mix until just combined.

Pour equal amounts of the cake batter into the two loaf pans. Bake in lower third of the oven for 45 to 55 minutes or until a knife inserted in the center comes out clean. Remove cakes from pans and transfer to a wire cooling rack. Allow cakes to cool completely. Before serving, dust with sifted powdered sugar, if desired.