Cream butter. Stir in sugar and vanilla sugar. Add egg and sour cream. Knead flour and baking powder well. Roll out the dough on a floured work surface as thick as the back of a knife and cut out 80-90 biscuits (approx. 3 cm in size).
Place on 3 baking trays lined with baking paper. Mix egg yolk and milk and brush the biscuits with it. Decorate with nuts, candied cherries and pistachios. Bake one after the other in a preheated oven (electric: 175 °C/ gas: level 2) for 7-8 minutes until light brown. Results in 80-90 biscuits