Many cake recipes instruct you to butter a cake pan and then flour it. We all know the butter stops the cake from sticking, but what does the flour do? The answer is twofold. The flour helps the cake batter grip the sides of the pan so that it rises evenly. It also creates a barrier between the butter and the batter to prevent the butter from melting into the batter. If you're making a chocolate cake, like the Triple-Chocolate Roulade from Fine Cooking #122, you can use cocoa instead of flour for coating the pan (or the parchment lining) so that there won't be a white film on the dark cake.