Put the butter it inside the mug you will be using.
Microwave the butter for 25-30 seconds until melted and hot.
Add the ingredients and mix well until everything is combined and without any lumps.
Microwave the cake for 60 - 70 seconds, depending on the power of your microwave.
Take the cup out of the microwave very carefully; it is better to cover your hand with a kitchen cloth. You can decorate your mug cake with sour cream or berries.,