It's like eating a jar of Nutella, except you don't have to feel bad about it.
Combine the flour, cocoa powder, baking powder, and salt in a ceramic mug.
Using a fork, beat in the egg, sugar and Nutella until thoroughly blended.
Microwave the mug on high for 75-90 seconds, or until the contents have risen and the center is set.
Let cool slightly, then serve.