Mix flour, sugar, baking cocoa, baking powder and salt in a greased cup. Add egg, milk and oil. Stir well with a fork. Place the mug on a saucer. Cook in the microwave at 800 watts for about 2 1⁄2 minutes.
Let the cake rest for 1-2 minutes. This can be served with peanut-sand cream and caramel sauce, for example.