Frost brownie with vanilla frosting. Place chocolate chips in small resealable food-storage plastic bag. Place in bowl of very hot water; let stand until chips are melted. Cut off tiny corner of bag. To make spiderweb, pipe melted chocolate on frosting in spiral pattern, starting at centre and keeping lines about 3/4 inch apart. Using toothpick or knife, draw lines outward through frosting, starting at centre of brownie.