I was going to post about mug cakes, then noticed this thread, and the comments about it being dry, so I thought I'd post here, because I do a mug cake myself, that's not too dry

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Grease one large coffee mug.
1 egg
3 tbsp plain flour
1 tsp baking powder
2 tbsp milk
1 tbsp sugar
1 tbsp unsweetened cocoa powder
2 tbsp nutella
1 and a 1/2 tbsp vegetable oil
Whisk with a fork till creamy.
In the microwave for 3 minutes(Based on 800 watt microwave).
It will probably rise over the cup.
It will be drier than a regular sponge cake, but it's still not too dry

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