Line 13x9-inch pan with foil; spray foil with cooking spray. In 1 1/2-quart saucepan, melt chocolate chips and 1/2 cup of the butter over low heat, stirring frequently, until smooth. Remove from heat. With wire whisk, beat in 1/2 package (4 oz) of the cream cheese until smooth. Spread in pan. Freeze until set, about 30 minutes.