Melt chocolate and margarine in 2-quart saucepan over very low heat; stir constantly just until melted. Remove from heat. (Or microwave chocolate and margarine in large bowl at high 2 minutes or until margarine is melted. Stir until chocolate is completely melted.)

Stir sugar into melted chocolate. Stir in eggs and vanilla until completely mixed. Mix in flour until well blended. Stir in nuts. Spread in greased 8-inch square pan.

CREAM CHEESE TOPPING:

In same bowl, mix cream cheese, sugar, egg and flour until smooth. Spoon over brownie mixture; swirl with knife to marbleize.

BAKE: Bake at 350-F for 35 minutes or until wooden pick inserted in center comes out almost clean (do not overbake!) Cool in pan; cut into squares.