Hot Dog Casserole

1 package deluxe macaroni and cheese mix (with cheese sauce, not powder)
1 onion, chopped
1/2 cup chopped celery
1 can cream of mushroom soup
1 cup grated sharp Cheddar
1 lb. hot dogs, sliced
1 jar sliced mushrooms, drained

Cook macaroni and cheese according to package directions; add grated Cheddar and stir until well blended. Stir in remaining ingredients and pour into a greased 2 quart casserole dish. Cover and bake at 350º for 30 minutes or until bubbly. Sprinkle with additional grated Cheddar and serve.