Mix flour and baking powder together in a mixing bowl or the bowl of stand mixer. Add butter and stir to combine until a crumbly dough forms.
Add sugar, vanilla sugar, and egg and beat until smooth.
Wrap dough in plastic wrap and refrigerate for approx. 60 min.
Chop chocolate and add to a bowl. Scald cream in a small saucepan and pour over chopped chocolate. Stir to combine, then let cool at room temperature.
Preheat oven to 180°C/350°F. Flour work surface and thinly roll out dough. Cut out cookies and transfer to a parchment-lined baking sheet. Bake for approx. 10 min., then let cool completely.
Beat cooled down chocolate cream again and transfer to a piping bag. Pipe cream over half of the cookies. Top with remaining cookies and press gently to seal. Enjoy!