1cupbuttermilk/sour milk(or, 1 tablespoon white vinegar + enough milk to equal a cup)
Instructions
Beat together butter, sugar, eggs, and vanilla until fluffy with an electric mixer. Add sour cream and beat to combine. Add half of the flour, baking soda, salt, and cocoa powder, mixing briefly to combine. Add buttermilk, mixing again, then add the rest of the remaining dry ingredients. Beat for 2 minutes on medium speed.
Pour batter into a well-greased stadium cake pan or other 12-cup tube/Bundt pan. Bake 45-50 minutes, until a toothpick stuck in the center comes out clean. Cool for 10 minutes, then remove cake from pan to a wire rack. Cool completely before decorating or serving.