Put 500 g flour in a bowl and press a depression in the middle. Add ##Schmand##. Spread butter in flakes on the edge of the flour and knead first with the dough hooks of the hand mixer, then with your hands until smooth.
Wrap in foil and chill for at least 1 hour.
Line three baking trays with baking paper. Preheat oven (electric cooker: 175 °C/circulating air: 150 °C/gas: level 2). Roll out the dough on a little flour to a thickness of about 1/2 cm. Cut out approx. 50 circles (approx. 6 cm Ø) (Attention - the dough is very soft!).
Cut out a small circle (approx. 2 cm Ø) from the centre of each one to form rings.
Whisk the egg yolk and 2 tablespoons of water. Brush the rings and the small circles with it, then sprinkle with sugar crystals and press on. Place all cookies on the trays.
Bake in a hot oven for 18-20 minutes one after the other. Let them cool down.