Preheat the oven to 350°F. Grease and flour three 6-inch cake pans and set aside.
Whisk or sift together the flour, cocoa powder, baking powder, baking soda, and salt.
In a separate large mixing bowl, whisk together the sugar, oil, and eggs until smooth.
Add the milk, sour cream, and vanilla. Stir together until smooth.
Add in half of the flour mixture to the batter and stir to combine with a large rubber spatula.
Carefully pour in the coffee and whisk until smooth. Repeat with the remains flour and coffee.
Evenly distribute the batter into the prepared pans. Bake in a preheated oven for 25 to 28 minutes or until a toothpick inserted into the center of the cakes comes out clean or with a few moist crumbs. Cool the cakes in their pans for 10 to 20 minutes before removing them from their pans. Continue to cool the cakes on a wire rack before storing, slicing, or frosting.