You need two boxes of cake mix. One can be any flavor you prefer, but the other MUST be Angel Food cake mix.
Mix them together. Then simply store the mixture in an airtight container until you get the urge for dessert. Then just put three Tablespoons of the dry mixture in a big coffee mug and stir in 2 Tbsp of water. Microwave it for one minute and you will have a single serving of cake.