Stir the softened butter until creamy. Mix with the powdered sugar and vanilla sugar. Add the cornstarch, flour, cocoa, cinnamon and cardamom. Knead into a smooth dough. Shape the dough into small balls, rolling in a hazelnut each time. Sit on the sheet. Bake at 180 ° C for about 12 minutes. Let cool down.
Cover with chocolate or cake icing, if you like. I used partly hazelnut glaze and partly vanilla glaze.