Add flour, cocoa powder, baking powder, and salt to a bowl and stir to combine.
Break chocolate into pieces and melt over a water bath. Add butter and stir well.
Beat eggs, sugar, and vanilla sugar in a large bowl until fluffy.
Add the chocolate-butter mixture and stir to combine. Gradually add the dry ingredients and mix until a tough dough forms.
Cover with plastic wrap and refrigerate for at least 2 hrs.
Preheat oven to 180°C/ 350°F. Form the dough into walnut-sized balls and roll them in confectioner's sugar. Place them on a baking sheet lined with parchment paper with approx. 3-cm/1.2-inch space in between and bake for approx. 12 min. Enjoy!