Preheat your oven to 190 degrees / Gas mark 5. Cream together the butter and sugar.
Cream together the butter and caster sugar.
Add the egg, flour and vanilla extract and stir until forming a biscuit dough. You may need to use your hands to ensure the dough forms a large ball.
Roll out the dough on a floured work surface until it's 1 cm thick. Cut out the biscuits and place onto a non-stick baking tray.
Bake for 8-10 minutes or until a slight colour change. Leave to cool.
Prepare your royal icing by whisking your egg white and gradually adding the icing sugar.
Separate into bowls and colour as required. Using a piping bag and thin nozzle to decorate your biscuits as desired. Use icing to attach googly eyes to the bat, cat and ghost.
Leave to set and enjoy!