Preheat oven to 350°F (175°C). Grease and flour two 9-inch round cake pans. Line the bottoms with parchment paper.

In a medium bowl, whisk together flour, cocoa powder, baking soda, and salt.

In a large bowl, cream together the softened butter and granulated sugar until light and fluffy.

Beat in the eggs one at a time, then stir in the vanilla extract.

In a small bowl, whisk together the buttermilk, red food coloring, and white vinegar.

Alternately add the dry ingredients and the buttermilk mixture to the butter mixture, beginning and ending with the dry ingredients. Mix until just combined.

Divide the batter evenly between the prepared cake pans.

Bake for 30-35 minutes, or until a wooden skewer inserted into the center comes out clean.

Let the cakes cool in the pans for 10 minutes before inverting them onto a wire rack to cool completely.

In a large bowl, beat together the softened cream cheese and butter until smooth.

Gradually add the powdered sugar, mixing until combined. Stir in the vanilla extract and milk (if using) until the frosting reaches the desired consistency.

Place one cooled cake layer on a serving plate. Spread a generous layer of frosting over the top.

Top with the second cake layer and frost the entire cake, including the sides.

Decorate as desired. Chill the cake for at least 30 minutes before slicing and serving.