1 med. onion, chopped
1 lb. ground beef
1/4 c. butter
3/4 tsp. salt
Pepper to taste
2 c. grated Cheddar cheese
1 (8 oz.) can tomato sauce
1 (3 oz.) can sliced mushrooms
1 (8 oz.) pkg. elbow macaroni, cooked & drained

Brown onion and beef in butter; add seasonings and cook about 15 minutes. Add 1 1/2 cups grated cheese and stir until cheese melts. Stir in 1/2 cup tomato sauce and mushrooms. Alternate layers of macaroni and meat mixture in 2 quart casserole. Top with remaining 1/2 cup tomato sauce and cheese. Bake at 350 degrees for 25 to 30 minutes.