Fallen Chocolate Cake

One large fallen chocolate cake can be prepared in either a springform pan or a cake pan with a removable bottom. Do not use a regular cake pan, as the cake will be impossible to remove once baked. To melt the chocolate and butter in a microwave oven, heat chocolate alone at 50 % power for 2 minutes; stir chocolate, add butter, and continue heating at 50 % for another 2 minutes, stopping to stir after 1 minute. If chocolate is not yet entirely melted, heat an additional 30 seconds at 50 % power. Though the cake is best when served warm, within about 30 minutes of being unmolded, it can also be held in the pan for up to two hours before serving.