Preheat oven to 350°F. Line 13x9-inch baking pan with foil, with ends of foil extending over sides of pan; grease foil lightly. Set aside. Microwave unsweetened chocolate and butter in large microwaveable bowl on HIGH 2 min. or until butter is melted; stir until chocolate is completely melted. Stir in sugar. Add all remaining ingredients except white chocolate; mix well. Pour into prepared pan.