Preheat the oven to 180°
In a large bowl mix the butter and the sugar first until the mixture gets pale and fluffy.
Then add the vanilla extract and the egg and mix again until you get an even dough.
Now you can add the flour, the baking powder and the cocoa powder. Mix until the dough gets an even dark brown color.
Roll rounded teaspoons of dough into balls, and place onto a baking sheet.
Try to flatten the cookies as much as possible. The cookies should have the same size as you will fill the vanilla cream in between.
Bake for 9 minutes, rotating once for even baking. Set baking sheets on a rack to cool.
Repeat until the entire dough is gone.