Preheat oven to 350°F. Line 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.
1 cup unsweetened cocoa powder, 1 cup brewed coffee , ½ cup sour cream, 1 teaspoon vanilla extract
In the bowl of a stand mixer with the paddle attachment or with an electric hand mixer, beat the butter until smooth and shiny, about 2-3 minutes. Add the granulated and brown sugars and continue beating until fluffy, and then beat in the eggs one at a time, mixing between each addition.
1 cup unsalted butter , 1 cup granulated sugar, ½ cup light brown sugar , 3 large eggs
In a separate bowl, whisk together the flour, baking soda and salt. Add the flour mixture to the butter mixture in thirds, alternating with the fudge mixture, mixing on low speed just until the flour is incorporated, scraping down the bowl several times as you go.
1 ½ cups all-purpose flour, 1 teaspoon baking soda, 1 teaspoon salt
Divide the batter between the cupcake liners, filling each cup halfway to the top and bake for 28 - 30 mins. A toothpick inserted into the center of the middle cupcake should come out with just a few moist crumbs on it when they are done. If there's batter on the toothpick, continue baking for a few minutes more.
Let the cupcakes cool before turning them out on a wire rack to cool completely before frosting.