1. In a medium mixing bowl beat the butter with an electric mixer on medium to high speed about 30 seconds.
2. Add the sugar, baking powder, baking soda, and salt. Beat until combined.
3. Beat in the egg, melted chocolate, and vanilla.
4. Beat in as much of the flour as you can with the mixer. Stir in remaining flour and the chocolate pieces.
5. Shape dough into two 12-inch-long-rolls. Wrap rolls in waxed paper; chill in the refrigerator at least 2 hours or up to 24 hours.
6. Cut dough into 1/4-inch-thick slices. Place slices 1 inch apart on an ungreased cookie sheet.
7. Bake cookies in a 375 degree F oven about 7 minutes or until edges are set. Cool on cookie sheet for 1 minute. Transfer cookies to a wire rack; cool.
8. Spoon Decorating Icing into a decorating bag fitted with a writing tip or fluted tip. Pipe icing into various size spiders or other Halloween shapes on cookies. Let cookies stand until icing is set. Makes 90 cookies.
Nutrition facts per cookie: 34 calories, 2 g total fat (1 g saturated fat), 5 mg cholesterol, 23 mg sodium, 5 g carbohydrate, 0 g fiber, 0 g protein.