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-heat, stirring constantly, until mixture comes to a boil. Boil for 1 minute. Remove from heat. Stir in 1½ 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.
NOTE: To transform Macaroni & Cheese from a simple dish to a savory one-dish meal, add 1 cup chopped ham or hot dogs after milk mixture comes to a boil.