I tried it again today, this time omitting the egg and adding an extra tbsp of milk. It did not rise as much, but it's both more moist and more fudgey. Excellent for those (hmo) who don't want to eat or throw away the leftover egg. And, it saves even more time and more dishes. Recommend.
So, official recipe:
4 tbsp:
Flour
Sugar
Milk
3 tbsp:
vegetable oil
chocolate chips
2 tbsp:
cocoa powder
and a dash of vanilla.
Microwave on high for 2 minutes and 30 seconds. Devour.
Total cook time: 5 minutes.
Total dirtied dishes: a mug, a tablespoon, and a fork.