Line two baking trays with baking paper. Cream softened butter, icing sugar and vanilla sugar with the whisks of the mixer. Stir in the egg and half the orange peel. Stir in flour and milk briefly.
Mix the remaining orange peel with sugar.
Preheat oven (electric cooker: 200 °C/circulating air: 175 °C/gas: see manufacturer). Pour dough into a piping bag with a medium star-shaped spout. Spray ice crystals (approx. 6 cm Ø each) onto the trays. Spray a wide tuff in the middle and 6 smaller tuffs around it.
Bake one after the other in a hot oven for about 8 minutes. Let them cool down.
Chop the couverture separately and melt each in a hot water bath. Dip half the biscuits up to half in white, the rest in dark chocolate. Sprinkle with the orange-peel-sugar mixture and leave to dry.