In another bowl, sift together the flour, cocoa powder, baking powder, baking soda and salt. Add half the dry ingredients into the butter mixture and mix on low speed. When dry ingredients are almost incorporated, stop the mixer and add the buttermilk. Continue to mix on low speed until all ingredients are almost incorporated. Stop the mixer and add the remaining dry ingredients. Mix on low until just combined. Spoon 2 tablespoons of batter into each cavity; spread batter to the edges. Cavity should be about 2/3 full.