Macaroni and Cheese (not the box kind)

My sweet friend Kristy Lee gave me this recipe. I made it once and now I have kiddos that refuse to eat "the kind from the box."

Macaroni and Cheese
2 tablespoons cornstarch
1 teaspoon salt
½ teaspoon dry mustard
¼ teaspoon pepper
2 ½ cups milk
2 tablespoons margarine or butter
2 cups (8 oz). shredded cheddar cheese, divided
2 cups dry macaroni noodles, cooked and drained.

Preheat oven to 375 degrees. In medium saucepan combine cornstarch, salt, dry mustard and pepper; stir in milk. Add margarine. Stirring constantly, bring to a boil over medium-high heat and boil 1 minute. Remove from heat. Stir in 1 ¾ cups cheese until melted. Add elbows. Pour into greased 2 quart casserole. Sprinkle with reserved cheese. Bake uncovered 25 minutes or until lightly browned.