To prepare a upside down brunch cake cake recipe, you first need to prepare your cake batter. You can use any cake mix that you have on hand, but if you don't have any, then you'll want to make your own. Preheat the oven to 350 degrees F (180 degrees C). Grease and flour two 8-inch round cake pans and set aside. In another large bowl, combine the flour, baking powder, salt, and baking soda. Add the dry ingredients to the wet ingredients and stir until combined. Pour the batter into the prepared pan and bake the cake for 35 to 40 minutes, or until the toothpick inserted in the center comes out clean. Allow the cakes to cool for 10 minutes before removing them from the pan.