Put flour, sugar, salt, lemon zest and egg in a bowl. Spread the fat in flakes and knead into a dough. Roll out the dough on a floured work surface and cut out about 60 fir trees (approx. 4 cm high).
Cut out the middle of half the cookies with a smaller fir tree cutter. Knead the rest of the dough, roll out again and cut out until the whole dough is used up. Place the cookies on 3 baking trays lined with baking paper.
Bake the trays one after the other in a preheated oven (electric cooker: 175 °C/ convection oven: 150 °C/ gas: level 2) for approx. 12 minutes. Remove and let cool off. Pass the jam through a sieve and spread it on fir trees.
Place the cut out fir trees on top and let them set.