Beat egg whites until stiff. Add sugar and continue to beat until well combined. With a rubber spatula, carefully fold under hazelnuts, vanilla sugar and vanilla extract. Using a teaspoon, scoop dough onto a cookie sheet lined with baking parchment. If using baking wafers, place cookie dough onto small round baking wafers (Backoblaten) and transfer onto cookie sheet. Place a whole hazelnut on top of each cookie.