To prepare a tiered chocolate buttercream cake recipe, first you need to prepare the cake batter. First, you'll need 2 cups of cake flour, 1 cup of baking powder, and 1 tablespoon of cocoa powder. Then, add 2 tablespoons of water to the dry ingredients and mix until they're just combined. Next, pour the batter into the prepared cake pan and bake it for 30 minutes at 350 degrees F. Remove the pan from the oven and let it cool for 10 minutes before serving.