Mix flour, sugar and salt in a bowl. Add egg and butter in pieces. Knead first with the dough hooks of the hand mixer, then with your hands to a smooth dough. Wrap the dough in foil and chill for about 45 minutes
Roll out the dough 2-3 mm thinly on a work surface dusted with flour. Cut out approx. 34 circles (6 cm Ø) each with a wavy edge and cut out fir trees (6 cm Ø), kneading the dough remains again and again, roll out and cut out the same way. Put the biscuits on 2 baking trays lined with baking paper. Bake in the preheated oven (electric cooker: 175 °C/ convection oven: 150 °C/ gas: see manufacturer) one after the other for approx. 12 minutes. Remove the cookies and let them cool down on a cake rack
Warm the jelly, spread it on 17 circles and fir trees and let it dry for about 1 hour. Stir icing sugar and egg white until smooth. Colour half of the jelly pink. Spread one half of the surface of each coated cookie (with jelly) with white icing and the other half with pink icing and immediately draw a zigzag pattern with the help of a wooden skewer. Let the cookies dry for about 1 hour
Simmer the rest of the jelly for about 1 minute, let it cool down until it gets a little firmer and spread it on the biscuits without the icing. Place the biscuits with the icing on top, press lightly and let dry for about 1 hour
waiting time approx. 4 hours