In a large mixing bowl, combine unsalted butter and caster sugar, beating until light and fluffy.

Gradually add in plain flour, cocoa powder, and black food coloring until a smooth dough forms.

Shape the dough into a disk, wrap in plastic wrap, and chill in the refrigerator for 30 minutes.

Dust your work surface lightly with flour. Roll out the dough to an even thickness of about 1 cm.

Cut out skeleton shapes and place them on parchment-lined baking trays. Chill the cut-outs for another 30 minutes.

Preheat the oven to 180°C. Bake for 18-21 minutes until edges are firm but centers are soft.

In a bowl, sift icing sugar and mix in water until thick and spreadable.

Transfer icing to a piping bag and decorate the cooled biscuits with spooky designs.