Preheat the over to 175C.
In a bowl mix butter with sugar, then add eggs (one at the time), then vanilla extract.
In a different bowl mix together flour, cocoa powder, baking powder and salt.
Mix in together wet and dry ingredients.
Take a piece of the mixture and create a ball in your hands, put it on a baking sheet and squish a bit (1 cm), and repeat.
Bake for 9 minutes. After, let it cool down before eating.