Whip the butter and cane sugar with the whisk of the hand mixer until creamy. Beat the egg. Mix oat flakes, almonds, baking powder and lemon peel. Gradually stir into the fat-egg cream. Wrap dough in foil and refrigerate for about 1/2 hour. Roll out the dough on a floured work surface to a thickness of about 0.5 cm.
Cut out 35 circles (6 cm Ø), knead the dough again and again and put it on 3 baking trays lined with baking paper. Bake one after the other in a preheated oven (electric range: 175 °C/ convection oven: 150 °C/ gas: level 2) for approx. 12 minutes. Pull the pastry with baking paper onto the cake rack and let it cool down. Colour each 50 g of sugar with food colouring to varying degrees, grind finer in the universal chopper and decorate the biscuits with different motifs (e.g. fir trees and stars)
1 hour waiting time