Directions

1. Preheat oven to 190°C/170°fan/Gas 5 and line 2 baking trays with baking paper. Cream butter with 150g (5oz) icing sugar until light and fluffy.
   Mix in vanilla extract and egg yolk, then fold in flour to form a firm dough. Wrap in clingfilm and chill for an hour.
   On a floured surface, roll out chilled dough to a 3mm (?in) even thickness. Cut out stars using a star-shaped cutter. Re-roll trimmings until all dough has been used up.
   Place on lined trays and bake for 10-12 minutes until golden brown. Cool on wire racks.
   In a wide, shallow bowl, mix remaining icing sugar with lemon juice and 3-4 tablespoons boiling water to make a glace icing.
   Squeeze 3 small blobs of each food colour over icing, then swirl together with a skewer to create a marbled effect.
   Dip cooled biscuits into icing, keeping as flat as possible, then place on wire racks to dry.