For the hazelnut stars, quickly knead flour with butter, sugar, egg, grated hazelnuts and cinnamon into a dough. Wrap in plastic wrap and let rest in the refrigerator for 1 hour.
Roll out the dough and cut out stars. Cut out an additional small star for half of the cookies. Place the cookies on a baking tray lined with baking paper and bake at 160 °C for about 10 minutes.
Let the cookies cool down and assemble them with jam. Sprinkle the cookies with powdered sugar.