Melt butter at low heat. Knead 225 g flour, 125 g sugar, vanillin sugar, 1 pinch of salt, liquid butter and milk first with a hand mixer and then briefly with your hands until smooth (the dough is very tender). Halve the dough. Form each half into a small roll (approx. 5 cm Ø) on a little flour. Wrap in foil, freeze for about 30 minutes
Whisk the egg yolk and 1 tablespoon of water. Spread dough rolls with it, roll in approx. 4 tablespoons of sugar. Cut into slices (a good 1/2 cm thick) and place on 1-2 baking trays lined with baking paper. Bake in the preheated oven (electric cooker: 200°C/circulating air: 175°C/gas: level 3) for about 12 minutes. Let them cool down