Mix together flour, sugar, vanilla sugar, salt and hazelnuts in a bowl. Zest the lemon and add zest to the mixture. Melt butter. Add melted butter and eggs to the mixture to form a dough. Wrap dough in plastic wrap and let rest at least 30 minutes in the refrigerator.
Preheat the oven to 170°C (approximately 340°F). Line a baking sheet with parchment paper.
Roll out dough to 0.3 cm (approximately 1/10 inch) thick and cut out cookies using a crimped circle cookie cutter. Cut a small circle (1 cm or 1/3 inch) in the center of half the cookies. Bake cookies for 8-10 minutes until light yellow. Allow to cool on a wire rack.
Meanwhile, heat raspberry jam. Spread jam on the whole cookies, topping each with a cookie that has the center removed to create a sandwich. Cool cookies completely and allow to dry for 1-2 hours. Sprinkle with powdered sugar and serve.