Midnight (or whenever) Mug Cake For 2

This recipe is billed as a late nigh snack, but I used it as a TGIF treat after work. My trusty oversized* narwhal mug was turned into a baking dish for the experiment.
This one is dangerously simple; load everything into the mug in stages, whisking along the way, then zap in the microwave.

Batter up.

It's cake in about 10 minutes. Victory.

Warm, gooey, and Delicious. 

Difficulty Level: Easy

Will It Get Made Again? This is the sort of thing that will hit a chocolate craving in less time than it would take to go to the store... So yes.

*The mug I made this in is 20oz. The recipe notes it usually spills over the edges of standard 16oz mugs, I went for cute with less clean-up.