Preheat oven to 375° F. Grease 2-quart casserole dish.
Combine cornstarch, salt, mustard and pepper in medium saucepan. Stir in evaporated milk, water and butter. Cook over medium-high heat, stirring constantly, until mixture comes to a boil. Boil for 1 minute. Remove from heat. Stir in 1 1/2 cups cheese until melted. Add macaroni; mix well. Pour into prepared casserole dish. Top with remaining cheese.
Bake for 20 to 25 minutes or until cheese is melted and light brown.
Macaroni and cheese like it's supposed to be, tasty with homemade goodness. Children and adults alike will love this classic!