WALNUT TOPPING: 1/4 cup (1/2 stick) margarine or butter 2 tablespoons all-purpose flour 3/4 cup firmly packed brown sugar 1 teaspoon vanilla 2 eggs 4 cups chopped walnuts HEAT oven to 350°F. MICROWAVE chocolate and 3/4 cup margarine in large microwavable bowl on HIGH 2 minutes or until margarine is melted. Stir until chocolate is completely melted. STIR granulated sugar into melted chocolate mixture. Mix in 4 eggs and 1 teaspoon vanilla until well blended. Stir in 1 cup flour. Spread in greased 13x9-inch pan. MICROWAVE 1/4 cup margarine and brown sugar in same bowl on HIGH 1 minute or until margarine is melted. Stir in 2 eggs, 2 tablespoons flour and 1 teaspoon vanilla until completely mixed. Stir in walnuts. Spread mixture evenly over brownie batter. BAKE for 45 minutes or until toothpick inserted into center comes out with fudgy crumbs. Do not overbake. Cool in pan; cut into squares. cook 54