Meanwhile, heat oven to 400°F. Grease 13x9-inch (3-quart) glass baking dish. Melt butter in medium saucepan over medium heat. Stir in flour until smooth. Gradually add milk, cooking and stirring until well blended. Cook 6 to 10 minutes or until mixture boils and thickens, stirring constantly. Stir in 1/2 cup Parmesan cheese and the pepper.