Microwave chocolate and margarine in large microwaveable bowl at HIGH 2 minutes or until margarine is melted. Stir until chocolate is completely melted. Stir sugar into melted chocolated until well belended. Stir in eggs and vanilla until completely mixed. Mix in flour until well blended. Stir in nuts. Spread in greased 13x9 inch pan. Bake at 180ºC or 35 to 40 minutes or until wooden pick inserted in center comes out almost clean (*Do not overbake*). Cool in pan; cut into squares. Makes 24 brownies.