Preheat the oven to 180C/160C Fan/Gas 4 and line a large baking tray with baking paper.

Put the butter and sugar in a bowl and beat until pale and fluffy. Add the egg yolk and vanilla and beat again until combined.

Tip in the flour and beat until it forms a soft dough.

Divide the mixture into 30g balls and flatten slightly. Push your index fingers into each dough ball to make two holes for the ?eyes?. Place the biscuits on the baking tray, leaving space between them to allow for spreading during baking.

Beat the jam to loosen it and fill each of the eye holes with jam, either with a teaspoon or with a piping bag.

Bake for 12 minutes until golden around the edges and leave to cool completely on the baking tray.

Transfer the melted chocolate to a small piping bag and cut a small hole in the end of it. Pipe a line for the mouth under the jammy eyes, and then pipe small vertical lines across the line to make it look like the mouth of a spooky skull.