Preheat oven to 350 degrees. Line a muffin pan with paper or foil liners. Stir together the flour, baking powder, baking soda, cocoa and salt. Set aside.
In a large bowl, cream together the butter and sugar until light and fluffy. Add the eggs one at a time, beating well with each addition, then stir in the vanilla. Add the flour mixture alternately with the milk; beat well. Fill the muffin cups 3/4 full.
Bake for 15 to 17 minutes in the preheated oven, or until a toothpick inserted into the cake comes out clean. Frost with your favorite frosting when cool.