Heat oven to 350°. Grease and flour rectangular pan, 13x9x2 inches. Stir together granulated sugar, baking mix, 1/4 cup margarine, 2 teaspoons vanilla, 4 squares melted chocolate and the eggs in medium bowl until moistened. Spread in pan. Bake 30 to 35 minutes or until edges begin to pull away from sides of pan; cool.