Combine flour, baking powder, sugar, vanilla sugar, salt, butter cut into pieces, egg and ground hazelnuts. Knead to a smooth dough and shape into a ball. Wrap in plastic wrap and refrigerate for 30 minutes.
Roll out dough on a floured surface until about 0.4 cm (approximately 1/5 inch) thick and cut out star-shaped cookies with a cookie cutter. Cut out small stars in the middle of cookies to fill with jam later on (being careful not to puncture dough at the base) Place cookies on a lined with parchment paper baking sheet and bake in preheated oven at 180°C (approximately 350°F) for about 12 minutes or until golden. Remove and allow to cool slightly.
Heat up jelly and fill small cookie stars with it. Allow to dry and sprinkle with powdered sugar. Serve.