In a microwave safe mug of about 9.30 fl oz (375 ml), mix the flour along with the cocoa powder, baking powder, salt and sugar.
Add in the milk, oil, vanilla extract and mix for a few seconds using a fork until you get a smooth.
Put it in the microwave and cook at high temperature from 90 seconds to 1 minute and a half until the mug cake rises and looks a bit firm on the top (the time will depend on the specific microwave). It is important not to overcook it so it is not hard, and be careful so it doesn't spill.
Take out of the microwave and let it cool down for 1 minute before eating. You can eat it along with some ice cream, fruit, whipped cream or chocolate frosting.
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