8: Cook one mug at a time (this is important) for 1 minute 30 seconds each at 850 Watts.
9: Leave to cool for a few minutes before eating as the cake will be boiling in the centre when you take it out of the oven.
Remarks
If you would like a lighter cake, add 1/4 teaspoon baking powder to the mixture. This is a great way to keep children amused on a rainy afternoon for a few minutes before teatime. As long as you take the mugs out of the microwave for them, there's no risk of them burning themselves.