If your cake has created a nice domed bottom or a "foot" and it's not setting flat on your serving tray, trimming the bottom may be your best option. Trimming the bottom works best while the cake is still in the cake pan. Using the edges of the pan as a guide, and with a sharp or serrated knife, cut through the cake removing the bottom. Don't throw it away however, you can crumble it up and serve it on top of the cake, or snack on it!