This recipe has been disseminated far wide on the internet. I tried it, and wish to state, for the record, that it works. The recipe is here:
Basically, you take one box of Duncan Hines ANGEL FOOD CAKE MIX WHITE and another boxed cake mix of any variety. Mix the 2 thoroughly, then store in an airtight baggie or container. It MUST be that particular boxed cake mix.
You mix 3 tablespoons of the mix and 2 tablespoons of water, zap for 1 1/2 minutes in a 700 watt microwave oven (the instructions say 1 minute for a 1100 watt oven, but mine is 700 watts, so not sure if this is correct for 1100).
I used an 8 oz coffee mug, zap 90 seconds, allow to sit for 15 minutes (very important). At the end, I was able to carefully tip out the cake from the mug onto a plate. I got something about the size of a cupcake. The texture was on the spongy side, kinda like those hot-milk-sponge-yellow-cake things you get at chinese dim sum shops.
Yes, recommend you try it: it will not fail; best of all, it will still be warm when you eat it.