Preheat the oven to 160°C / 325°F / Gas mark 3.
Prepare 2 baking trays with greaseproof paper and set aside.
In a bowl, add the butter and beat with a wooden spoon until smooth.
Add the flour, icing sugar and orange zest and beat together to make a soft dough.
Knead into a ball and wrap in cling film.
Chill for 1 hour.
Roll the dough out on a lightly floured surface to 3mm.
Cut 24 circles with a 7.5 cm round plain cutter.
Place them on the baking trays.
Using a small sharp knife to out Halloween faces on 12 of the circles.
Collect the spare biscuit dough and shape stems trimming with a sharp knife.
Press to the top of each biscuit to join.
Bake all the biscuits for about 15 minutes until pale golden.
Leave to set for a while, then cool completely on a wire rack.
Mix the icing glaze ingredients to make a smooth, icing, adding a bit more juice if needed, then set aside.
For the filling, beat the mascarpone with the icing sugar, then stir in the cooled melted chocolate.
Spread the filling over the cooled plain biscuits, then press the Halloween faced ones on top.
Do this just before you want to eat them.
Brush with the icing, using a clean paint brush or pastry brush.
Eat the same day.