Cut butter into small cubes. Separate egg. Knead butter, sugar, salt, egg yolk and almonds with the dough hooks of the hand mixer. Add flour and knead with your hands to a smooth dough.
Form short pastry into a ball, wrap in foil and chill for about 1 hour.
Shortly knead the short pastry and roll out to a thickness of approx. 5 mm on a floured work surface. Cut out hearts in different sizes (5 cm Ø,1 cm Ø), knead and cut out the dough again and again until everything is used up and put it on 2 baking trays lined with baking paper.
Bake in the preheated oven (electric cooker: 175 °C/ convection oven: 150 °C/ gas: see manufacturer) for 10-12 minutes.
Mix icing sugar and 9 tablespoons of water to a smooth glaze. Put 3 tablespoons into each bowl and colour with different food colouring. Brush the biscuits with the icing. Decorate with sugar stars.