Line cookie sheet with waxed paper. In 1-cup microwavable measuring cup, microwave baking chips uncovered on Medium (50%) 30 seconds. Stir; microwave in 10-second increments, stirring after each, until melted and smooth. Place in small resealable food-storage plastic bag; seal bag. Cut off tiny corner of bag. Squeeze bag to pipe star and squiggle shapes as desired on waxed paper; immediately top with sprinkles. Refrigerate 10 minutes to set.