Mix butter, icing sugar, marzipan, vanillin sugar and lemon zest. Sift the flour over the mixture and knead. Form a roll (approx. 4 cm Ø) and let it rest in the refrigerator overnight. Spread the dough roll with whisked egg yolk and roll in the sugar. Cut into slices of about 1/2 cm thick. Place on a baking tray lined with baking paper. Bake in a preheated oven (electric cooker: 175 °C/ convection oven: 150 °C/ gas: level 2) for 10-15 minutes