Preheat oven to 350°F.
Line a 6-cup muffin pan with cupcake liners or place paper cupcake cups on a sheet tray and set aside.
In a medium bowl, whisk together the cocoa powder, coffee, sour cream, and vanilla to make a shiny fudge. Set aside.
⅓ cup unsweetened cocoa powder, ⅓ cup brewed coffee, 2 tablespoons sour cream , ½ teaspoon vanilla extract
In the bowl of a stand mixer, beat the butter until smooth and shiny, about 2-3 minutes.
⅓ cup unsalted butter
Add the granulated and brown sugars and continue beating until fluffy, and then beat in the egg, mixing well.
⅓ cup granulated sugar, 2 tablespoons light brown sugar, 1 large egg
In a separate bowl, whisk together the flour, baking soda, and salt.
½ cup all-purpose flour, ¼ teaspoon baking soda, ¼ teaspoon kosher salt
Add the flour mixture to the butter mixture in thirds, alternating with the fudge mixture, scraping down the bowl several times as you go.
Divide the batter between the cupcake liners and bake for 22- 25 mins.
A toothpick inserted into the center of the middle cupcake should come out clean when they are done.
If there’s batter on the toothpick, continue baking for a few minutes more until it comes out clean.
Let the cupcakes cool before turning them out on a wire rack to cool completely before frosting.