Line 13x9-inch pan with foil, with ends of foil extending over sides. Grease foil.
Microwave chocolate and butter in large microwaveable bowl on HIGH 2 min. or until butter is melted. Stir until chocolate is completely melted. Add 2 cups sugar; stir until well blended. Add 4 eggs; mix well. Stir in 1 cup flour until well blended; spread into prepared pan.
Beat cream cheese and remaining sugar, egg and flour in same bowl with whisk until well blended. Spoon over brownie batter; swirl gently with knife.
Bake 35 to 40 min. or until toothpick inserted in center comes out with fudgy crumbs. (Do not overbake.) Cool completely. Use foil handles to lift brownies from pan before cutting to serve.