Meanwhile, in 2-quart saucepan, heat 2 tablespoons butter, the corn syrup and water to rolling boil, stirring frequently; remove from heat. Stir in 2 oz chocolate until melted. Stir in 1 teaspoon vanilla and the powdered sugar. Beat with spoon until smooth. Frost chilled bars with Chocolate Frosting. For bars, cut into 6 rows by 6 rows. Store covered in refrigerator.