Peel and slice potatoes and onions very thin. Butter bottom and sides of a casserole dish. Put potatoes and onions in dish in layers. Thin layers. After each salt and pepper and season salt (if desired) and chunks of butter. Repeat layers. Bake, covered in 400 degree oven about 1 hour. Or until potatoes are tender. Loosen sides and turn out on oven proof platter. Sprinkle with Parmesan cheese and return to oven for 5 minutes.

Vidalia onions are very juicy so browning will not be as great as with other onions. But the flavor is great even for people who do not care for onions.