Mix butter, both kinds of sugar and salt in a bowl with the whisk of the hand mixer. Mix flour, spices and baking powder. Whisk the egg and milk and alternately stir in the flour. Wrap the dough in foil and chill for approx. 30 minutes
Roll out the dough 2-3 mm thinly on a floured work surface. Cut out biscuits (e.g. stars, snowflakes, hearts and fir trees) and spread them on 2 baking trays lined with baking paper. Bake in the preheated oven (electric cooker: 175 °C/ convection oven: 150 °C/ gas: see manufacturer) one after the other for 10-15 minutes. Take out biscuits and let them cool down
Sieve the icing sugar into a bowl. Stir in first egg white, then lemon juice until a thick, smooth glaze is formed. Divide the icing into as many bowls as colours are desired. Add 1-2 drops of food colouring to each bowl (mix colours if necessary). Apply the glaze to the cookies with a brush and let it dry for at least 1 hour
waiting time approx. 1 1/2 hours