This dish must be started first thing in the morning.
Cook 6 or 7 medium - large potatoes with skins on - cool & put in large ziplock plastic bag in refrigerator until cold & firm (approximate 2 + hours or more). Once potatoes are cold carefully peel off skins. On a large coarse grater grate potatoes into a large bowl.
Thinly slice one large sweet onion and chop into pieces. In a skillet carefully brown onion in 2 T. butter until yellow & limp, add to grated potatoes with 2 cans of Cream of Celery soup plus 1 cup Half & Half. Combine thoroughly and place in a baking dish, cover dish with lid to let stand all day in refrigerator. (very important for soaking in moisture!) Prepare cracker crumb topping as follows:
Cracker Crumb Topping: combine in a bowl 1 cup crushed buttery flavored cracker crumbs (either Ritz or Town House type crackers), 1 T. melted butter, 2 T. grated Parmesan cheese. Sprinkle cracker crumb topping over top of potato mixture. Bake in a preheated 350 degree oven for 45 minutes. Either serve hot from oven or cold from frig next day.