Cream together the butter and sugar. Add the eggs and mix well. Mix in the sour cream and vanilla.
In a separate bowl whisk together the flour, cocoa, espresso powder, and baking powder.
Add ⅓ of the dry ingredients to the wet ingredients. Add half the milk. Repeat, until all the ingredients are incorporated. Stir in the chocolate chips.
Add to muffin pan lined with cupcake liners sprayed with non-stick cooking spray.
Bake for 18-22 minutes.
Mocha Coffee Frosting
Cream butter. Add sugar, espresso powder, and cocoa powder. Thin with milk, if needed.