In small microwavable bowl, place chocolate chips and shortening. Microwave on High 30 to 45 seconds; until chips can be stirred smooth. Place into resealable food-storage plastic bag; partially seal bag. Cut small tip from corner of bag; drizzle over frosting. Refrigerate about 15 minutes or until chocolate is set. Cut into 4 rows by 4 rows. Store covered at room temperature.