Mix flour, sugar, vanillin sugar, rum flavouring, bitter almond oil, cardamom, cold butter, salt and ground walnuts with the dough hooks of the hand mixer to a smooth dough. Cover the dough and put it in a cool place overnight. Divide the dough. Roll out one half on a floured work surface to a thickness of approx. 1 cm and cut out round cookies (4 cm Ø). Place the cookies at a distance on 3 baking trays lined with baking paper. Bake the trays one after the other in a preheated oven (electric range: 200 °C/ convection oven: 175 °C/ gas: level 3) for approx. 10 minutes. Let them cool down on a cake rack.
Repeat the process with the second half of the dough. Knead the marzipan and roll out thinly between 2 layers of foil. Cut out round taler the size of the cookies. In the meantime, let the chocolate icing soften in a hot water bath. Spread the top of the biscuits thickly with currant jelly, place a marzipan taler on top and press carefully. Dip the marzipan side into the dissolved chocolate icing and cover with 1/2 walnut. Allow to dry completely before serving