These are sugar cookies that I made last Halloween in the ghost shape, decorated with royal icing.
As usual, I start with sugar cookies made from scratch using this recipe: Sugar Cookies
Then I decorated them with this royal icing recipe: Royal Icing
To decorate them, I first piped on white royal icing as the base and let it dry overnight. Then I piped on the hat, face and word "Boo" with purple, green and orange icing and let the icing dry overnight before packaging them up in clear treat bags, tied with co-ordinating ribbon.