Beat the butter, sugar, vanilla sugar and salt for 3-4 minutes until fluffy. Add the flour and quickly combine into a dough. Chill for at least 30 minutes.
Roll out the dough on a little flour to about 5 mm thick. Cut out the cookies in a mirror shape with a pointed knife and place on a baking tray lined with baking paper. Chill for 15 minutes.
Preheat the oven to 190°C bottom/upper heat. Bake the Guetzli in the middle of the oven for 10-12 minutes until light. Allow to cool.
For the glaze, stir powdered sugar with lemon juice to a thick paste. Pour about 1⁄3 of the mixture into another container and color it egg yolk yellow with food coloring. Pour the yellow icing into a small piping bag without a nozzle, for example.
Cover the cookies with a thick layer of white icing and allow to dry. Then, using the yellow icing, pipe a large yellow dot on top as an “egg yolk”.
Let the cookies dry well. Store in a cool place until ready to serve.