Combine flour, cocoa, sugar and chocolate in a tall mug and stir with chopsticks.
Add the beaten egg and mix well. Pour milk and oil, and mix some more. Microwave for 2-2.5 minutes at 700W.
When the cake stops rising, stop the microwave, and check with a skewer to see if it's completely cooked through.
To prevent the mixture from boiling over, keep your eye on it while microwaving, and turn the microwave off accordingly. I used a 400 ml mug.
Story Behind this Recipe
I created this recipe because I wanted a small portion of cake and I wanted to make something quickly! I didn't want to do a lot of dishes and I didn't feel like using the oven in this heat!
The microwave time varies on the mug, so check doneness of the cake with a skewer. Turn off the microwave right before the mixture is completely cooked. Leave the cake in the mug and let it cook in residual heat. This will help the cake become extra-moist.