Preheat the oven to 175ºC/350ºF/ Gas Mark 4. Generously grease two baking sheets. Combine the butter, sugar and vanilla extract in a food processor until smooth.
Add the sifted flour, spices, egg and egg yolk and process to a smooth dough. Wrap in parchment and refridgerate until firm.
Roll out the dough on a lightly-floured work surface to 6mm in thickness. Cut out large star shapes using cutters, then cut out smaller stars from the centres of each.
Place on the baking tray. To make stained glass biscuits, break up boiled sweets and place in the holes in the middle of the stars before cooking.
Bake for 10-12 minutes until golden. Allow any stained glass biscuits to cool completely on the tray before removing them to a wire rack.
Decorate the biscuits as desired. Allow them to set.