Combine all ingredients in a cup and mix with a spoon until lumps are gone.
Then place the cup in the microwave and bake at full power for 1 1/2-2 minutes.
If you don’t have a microwave, you can also prepare the cup cake in the oven at 170 °C top/bottom heat. It will be semi-runny after 15 minutes, soft to the core after 20 minutes, and cooked through after 25 minutes.
It is best to enjoy the cup cake while it is still warm.