In a large bowl, beat butter and sugar until light and blended. Beat in egg and vanilla. In another bowl, whisk flour, baking powder and salt; gradually beat into creamed mixture. Shape dough into 2 portions. Shape each into a disk; wrap and refrigerate 1 hour or until firm enough to roll., Preheat oven to 350°. On a lightly floured surface, roll each portion of dough to 1/4-in. thickness. Cut with floured 2-1/2-in. Halloween-shaped cookie cutters. Place 2 in. apart on ungreased baking sheets. Bake 8-10 minutes or until edges are light brown. Remove from pans to wire racks to cool completely., In a large bowl, beat confectioners’ sugar, shortening and enough water to reach spreading consistency. Tint frosting and decorate as desired. Let stand until set.