Preheat oven to 350 degrees. In a medium bowl, mix together flour, salt, and baking soda and set aside. In a mixing bowl, cream together butter and shortening. Add sugars until well combined. And egg and vanilla and beat until fluffy. Add the flour mixture, a little bit at a time, stirring until combined. Drop 1 1/2″ dollops onto cookie sheet. Press one candy melt into your dough. Bake 10-11 minutes and follow steps above to get your spiders.