Squash Casserole

4 medium yellow squash, peeled and sliced
3 cups shredded carrots
2 cups herbed stuffing
1 cup chopped onion
6 tablespoons butter or margarine
1 cup sour cream
1 can condensed cream of celery soup

Cook squash until tender and set aside. Cook carrots and onion in butter, until tender. Stir in 1 1/2 cup stuffing, soup and sour cream. Stir in squash. Pour into lightly oiled 1 1/2 quart casserole dish. Melt 2 tablespoons butter; add rest of stuffing. Put on top of casserole. Cook at 350° for 35 minutes.