Mix 300 g flour, rye flour and spice. Heat honey in a pot (to approx. 60 °C, do not boil!). Add to the flour mixture and knead everything well by hand. Knead in cane sugar and crumble candy. Dissolve salt of hartshorn in 1 tbsp. cold water. Add to the dough with egg yolk and potash and knead well again. Wrap the dough in foil and chill for about 1 hour.
Preheat oven (electric cooker: 180 °C/circulating air: 160 °C/gas: see manufacturer). Line two baking trays with baking paper. Roll out dough in portions on a floured work surface to a thickness of approx. 4 mm. Use a cookie cutter to cut out fir trees (approx. 7 cm high) and place them on the baking trays. Bake in a hot oven for about 12 minutes one after the other. Remove and pull from the baking tray with the baking paper. Let it cool down.
Mix icing sugar and lemon juice to a smooth glaze. Brush fir trees with it and decorate with sugar pearls. Leave to dry.