At the request of the lovely Wildly Parenthetical (a screen name of which I have always been jealous), I am reproducing here, utterly without permission, a recipe given to me this evening at Belly Dancing. (If you know the source, please let me know, I will credit - or remove if required.)
4 tbsp flour
4 tbsp sugar
2 tbsp cocoa
3 tbsp milk
3 tbsp oil
3 tbsp chocolate chips (optional)
a small splash of vanilla extract
1 large coffee mug
Mix dry ingredients in coffee mug well. Add the egg and mix thoroughly. Add milk and oil and mix well. Add the chocolate chips (if using) and vanilla extract and mix again.
Put your mug in the microwave and cook for 3 min at 1000W (high). The cake will rise over the top of the mug, but don't be alarmed!
Allow to cool a little, and tip out onto a plate if desired. EAT.
I suspect you might have worked out that last step yourself.