Beat eggs, butter, sugar and vanilla sugar until frothy. Add eggs one at a time. Slowly add the grated chocolate and the lukewarm milk. Fold in the hazelnuts and slowly fold in the sifted flour with the baking powder.
Grease the wreath cake mold (diameter 28cm), pour in the batter.
Bake at 180 degrees / convection 160 degrees for about 60 minutes.
Let something cool in the tin, then turn out onto a wire rack.