Grab two mugs! The smaller it is the more the cake overflows and looks all pretty, if you are like us, and have slightly bigger mugs, you won't see the effect of how much it can rise! :)

Begin by softening the butter in the mugs for about 10-15secs, make sure you don't melt it. Next stir in 2 tbsps of sugar until its fluffy and creamy - it doesn't take long probably 30 seconds

If you are going with the egg, stir it up in a ramekin and divide it between the two mugs. If you are not using the egg, then go to the next step

Add 2 tbsps of sour cream, and a few drops of vanilla (don't pour lots!). Stir in the 1/4 cup of flour and 1/8 tsp baking powder and mix it all up. You should now have a cake batter type consistency

For the crumb topping!: Mix 1 tbsp of butter, 2 tbsps flour, 1 tbsp brown sugar and 1 tsp of cinamon. Smoosh it together with your fingers to form lumps. Add this crumb topping mixture to your cup

In the microwave it goes for a minute first, then do 10 or 20 seconds extra and that's it. It will be hot, so don't get super excited and dig into it like K did :)