I've seen this question about how to alter a chocolate cake recipe to make a plain cake, my question is the other way around, how to alter a vanilla cake recipe to make a chocolate cake? I read in a website that replacing 1/2 cup of flour with cocoa powder would do, is that right? I'd like to know a formula to use for every recipe but in case that is not possible and depends on the recipe one is using, here is the recipe for my vanilla cake:
4 eggs
1 and 1/2 cups sugar
1 cup oil
1 cup buttermilk
2 and 1/2 cups flour
2 and 1/2 tsp baking powder
1 tsp baking soda
1 tsp vanilla powder