Put flour, 100 g icing sugar, 1 pinch of salt, flavour, butter in pieces, 1 egg and possibly 1 tbsp. cold water in a mixing bowl. Knead first with the dough hooks of the mixer and then briefly with your hands to a smooth dough.
Wrap in foil and chill for about 1 hour.
Line two baking trays with baking paper. Roll out the dough on some flour 4-5 mm thick. Use an ice crystal cutter (approx. 7 cm Ø) to cut out about 30 ice crystals and spread them on the baking trays.
Whisk 1 egg yolk and milk. Spread the biscuits with it and sprinkle with decorating sugar. Bake one after the other in a preheated oven (electric oven: 175 °C/circulating air: 150 °C/gas: see manufacturer) for about 10 minutes.
Let it cool down. Dust with a little icing sugar.