Vidalia Onion Casserole

5 large onions (Vidalia, if possible)
1/2 cup (1 stick) margarine
Parmesan cheese
Crispy buttery crackers

Peel and slice onions into thin rings. Saut? in margarine until limp or opaque. Pour half of onions into 1 1/2-quart casserole. Cover with Parmesan cheese, then crushed crackers. Repeat layers and bake uncovered in 325 degree F oven until golden brown, about 30 minutes.