4 teaspoons butter, 2 cans condensed Cheddar cheese soup, 1 cup milk, 1 (8 oz) cream cheese, 2 cups shredded mild cheddar cheese, 6 cups cooked elbow macaroni.
Melt butter over medium heat in large sauce pan. Add onion, saute for 2 minutes until tender. Whisk in soup, milk, cream cheese and half of cheddar cheese, stirring just until cheese melts. Stir in macaroni and pour into casserole dish. Top with remaining cheese.
Bake at 350 degrees for 45 minutes.