Heat butter in a pot until slightly frothy, pour into a bowl and let it cool down. Stir until foamy. Add sugar, vanillin sugar and salt. Mix flour and baking powder, stir in.
Form two thick dough rolls (approx. 4 cm Ø) and roll them in chopped cashew nuts. Press on well. Wrap in foil and put in a cool place for about 1 hour. Cut off thalers of about 3/4 cm thickness. Press a cashew nut in the middle of each.
Whisk the egg yolk and 2 tablespoons of water and coat the thalers with it. Bake in the preheated oven (electric oven: 200 °C/ gas: level 3) for 8-10 minutes. Let it cool down on a cake rack.
Results in about 32 pieces.