Preheat the oven to 350°F. Butter two 8-inch round cake pans. Sprinkle about ½ tablespoon of flour in each pan, tapping the sides of the pan while tilting it slowly in a circle to spread the flour evenly over the butter. Tip the pans over the sink, one at a time, to tap out any excess flour. Set aside In a medium bowl, whisk together the cocoa powder, brewed 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, beat the butter until smooth and shiny, about 2-3 minutes.
1 cup unsalted butter
Add the granulated and brown sugars and continue beating until fluffy, then beat in the eggs one at a time, mixing well between each addition.
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, scraping down the bowl with a spatula several times as you go.
1 ½ cups all-purpose flour, 1 teaspoon baking soda, 1 teaspoon kosher salt
Divide the batter evenly between the prepared cake pans and bake for 25 - 28 minutes. A toothpick inserted into the center of the cakes 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 cakes cool in their pans for 10 minutes before turning them out on a wire rack to cool completely before frosting.