Preheat oven to 350 degrees and line a 12-cup cupcake pan with cupcake liners.
In a bowl, combine cocoa and hot coffee together, whisking until smooth. Set aside.
With a standing mixer or hand mixer, beat butter until creamy and fluffy, about 2-3 minutes.
Next, gradually add in granulated sugar and brown sugar, beating 2-3 minutes until it is light and fluffy.
Add eggs, one at a time, beating just until the yellow disappears.
Add in the chocolate/coffee mixture, and beat until just combined.
In a separate bowl, sift together flour, baking soda, baking powder, salt, and espresso powder. Set aside.
Next, stir together buttermilk, vanilla extract, and sour cream.
Alternately add the buttermilk mixture and flour mixture to the butter batter, beginning and ending with the flour mixture. Do not overmix.
Divide batter evenly between muffin cups (the batter makes 14-16).
Bake for 17-18 minutes, or until a cake tester comes out clean. Be careful not to over-bake, as chocolate cupcakes can get very dry if over-baked.
Allow to cool.