Separate the egg. Chill the egg white. Mix 400 g flour, sugar, cocoa, spices and soda in a large mixing bowl. Add egg yolk, sugar beet syrup and butter in flakes. Knead with the dough hook of the hand mixer.
Place the dough on the floured work surface and work into a smooth dough with floured hands. Wrap in foil and chill for about 1 day.
Line 4 baking trays with baking paper. Divide the dough into 4 portions and roll out one after the other on some flour about 0.5 cm thin. Knead the rest of the dough again and again.
Cut out dough with different heart-shaped cutters (diameter 5-7 cm). Distribute on the trays. Bake one sheet at a time in a preheated oven (electric cooker: 175 °C/ convection oven: 150 °C/ gas: see
manufacturer) Bake for 10-12 minutes. Remove and let cool on cake racks.
For the decoration mix lemon juice and icing sugar to a smooth glaze. Cut the icing in half or in thirds as desired. Colour 1 or 2 parts of the icing with food colouring. Pour the icing into freezer bags and cut off a small corner each.
Decorate cookies with icing. Decorate with sugar pearls and stars etc. and let dry.