Place ingredients in medium microwave safe bowl. Microwave on high in 20 second intervals until the chocolate chips are melted. Stir after each 20 second interval to avoid burning. If desired add 1/2 tsp vanilla extract and add-ins of choice. Stir to fully combine. Spread into a lined 8 x 8 inch cake pan. Place in the refrigerator for 1 hour or until firm. Remove and cut into desired size pieces