Mix the softened butter and caster sugar together in a large bowl using a spoon. Add the egg yolk and orange zest and stir until mixed.

Sift together the flour and cocoa and add to the buttery mixture and stir well until all the ingredients are combined and stick together to form a dough.

Cover and refrigerate for about 30 minutes or until quite firm. Roll out the dough on a very well floured surface to about the thickness of a two pence piece. Cut out the dough using a star shaped cutter and place on baking sheets lined with non stick baking paper. Re-roll any off cuts and repeat. Other festive shaped cutters can also be used.

Bake at 180 °C/160 °C fan/gas mark 4 for about 10 minutes for mini biscuits or until the edges are just beginning to brown. Larger biscuits may take 2-3 minutes more. Allow to cool before decorating. Dust the biscuits lightly with a little icing sugar and finely drizzle with the melted chocolate. Allow the chocolate to set before serving. Can be stored in an airtight container for up to three days.