Mix the butter with sugar and vanilla sugar until frothy, gradually add the egg yolks. Mix the flour and baking powder and knead together with the grated chocolate into the butter, egg and sugar mixture.
(If the dough is very soft, refrigerate briefly before further processing.)
Shape the dough into small balls (the size of a walnut) and place them on a baking sheet lined with baking paper with a little space between them.
Bake at 200 - 220 ° C for about 10 minutes, the cookies should be light brown.
Freshly baked they are still very crunchy, we like them best when they are a little more crumbly - stored in tin cans for some time.