Mix the butter, sugar, egg yolk and salt until frothy. Sift the flour and baking powder and knead a dough. Wrap the shortcrust pastry in foil and refrigerate.
Knead individual dough portions until smooth. Roll out about 3 mm thick and cut out round cookies 6 cm in diameter. Place on baking paper, brush with whisked egg white and sprinkle with cinnamon sugar.
Bake at 160 ° C for about 10-15 minutes until golden.