Butter around 25g
Heat butter and chocolate in a bowl which is in hot water.
Keep stirring till they melt.
Remove them from hot water to get cool.
Whip an egg with around 15g sugar till the color becomes light.
Do make sure the chocolate is cool already.
Put around 15g flour into the mixture. Stir evenly. Then put the bowl into fridge for 30 minutes.
Brush butter onto the inner wall of baking bowl.
Pour the chocolate mixture into baking bowl.
Put into oven for ten minutes.
When there are some small cracks on the surface of cake, the cake can be removed from the oven.
If you like, you can spread some icing sugar.
Try to scoop it with a small spoon.
And you will be surprised!