Mix flour and salt in bowl.
Beat butter in another bowl until creamy, 3 minutes. Beat in sugar until light and fluffy, about 3 minutes. Beat in egg. Using wooden spoon, stir in flour mixture. Stir in candies. Divide dough in half; shape each half into 4 x 4-inch square. Wrap each in plastic wrap. Chill until firm, about 2 hours.
Heat oven to 350 degrees F. Coat baking sheets with nonstick cooking spray.
Roll out dough, half at a time, between 2 sheets of waxed paper into 12 x 10-inch rectangle, 1/8-inch thick. If dough is too soft, refrigerate until firm. Cut each half into 2-inch squares. For each square, cut diagonally from each corner toward center, about 3/4 inch. Turn down alternate corners of each cookie, placing tips in center to create a pinwheel effect. Place cookies, 1 inch apart, on prepared baking sheets.
Bake in 350 degree F oven 6 to 8 minutes or until firm; watch carefully so edges of cookies do not overbrown. Remove cookies to wire racks to cool.
When cooled, fill pastry bag fitted with 1/4-inch writing or star tip with frosting. Pipe medium-size dot in center of each poinsettia. Dip frosting into sprinkles to cover dot. Let stand until set. Store in airtight container at room temperature up to 5 days. Makes 5 dozen cookies.
Using powdered egg whites, follow package directions for preparing equivalent of 1 egg white. In a bowl beat prepared egg white mixture and cream of tartar until foamy. Gradually beat in confectioners sugar; continue beating until thick and creamy, 2 to 3 minutes. Cover until ready to use.