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Preheat oven to 350 degrees. Line a 12-tin cupcake pan with cupcake liners (if you plan on doing minis, line a mini pan with mini cupcake liners).
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Combine cocoa and hot coffee together, stirring until smooth; add in oil and stir; set aside.
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Beat butter with a standing mixer or hand mixer until creamy and fluffy, about 2-3 minutes. Gradually add in white and brown sugar, beating 4-5 minutes until it is light and fluffy. Add eggs, 1 at a time, beating just until the yellow disappears.
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Add in chocolate/coffee mixture, and beat until just combined.
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In a bowl, sift together flour, baking soda, baking powder, salt, and espresso powder.
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Stir together buttermilk, vanilla extract, and sour cream (or Greek yogurt).
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Alternately mix the buttermilk mixture and flour mixture with the butter batter, beginning and ending with the flour mixture. Do not overmix.
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Divide batter evenly between muffin cups (the batter makes 14-16).
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Bake for 17-18 minutes, or until a cake tester comes out clean. Be careful not to overbake, as chocolate cupcakes can get very dry if overbaked (for the minis, bake for 10-12 minutes).
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Allow to cool.