Preheat your oven to 350 degrees, and grease a 10 cup tube pan or two large loaf pans. Set aside. 

In a large bowl, beat together the butter, sour cream, and sugar until smooth. Add in the eggs, two at a time, and then the vanilla, beating until the mixture is fully combined. 

In a medium bowl, whisk together the flour, baking powder, instant espresso powder, salt, and cocoa powder. Add the flour mixture in several additions to the butter mixture, alternating with the milk, mixing well between each addition. Beat until the mixture is smooth- the batter will be fairly thick. 

Pour the batter into your prepared pan(s) and spread evenly. Bake in your preheated oven for 60-65 minutes, or until a cake tester comes out clean. (Note that loaf pans will take slightly less time to bake, start checking at 45 minutes) Cool and enjoy!