In a saucepan melt and saute until soft and slightly carmelized:
2 tablespoons unsalted butter
2 medium onions, thinly sliced
Set aside for later.
In a heavy saucepan melt and blend together until slightly browned and forming a roux (approx. 3 minutes)
6 tablespoons unsalted butter
6 tablespoons flour
Add in a slow continuous stream , stirring constantly and bringing the sauce to boil for about 1 minute:
3 1/2 cups milk, scalded
salt and pepper to taste
Reduce to low
Meanwhile using a mandoline or very fine steel slicing blade (1/8 inch thick) Slice and set aside:
1 1/2 pounds boiling potatoes, peeled
Slice and set aside:
1 medium celery root, peeled
In a large buttered baking dish, at least 2 1/2-inches deep, spread 1/3rd of the white sauce over the bottom of the dish and then arrange 1/2 the potato slices in a single layer, slightly overlapping. Spread 1/2 the onions over the potatoes and top with 1/2 the celery root.
Spread more sauce over the celery root and sprinkle all with:
1 cup coarsely grated white New York Cheddar, or Romano cheese
Arrange in a single overlapping layer:
1 pound HoneyBaked Ham, cut into 1/4-inch slices
Repeat above layering of ingredient (Potatoes, Onions Celery Root White sauce) and top all with:
1/2 cup dry bread crumbs
1 more cup coarsly shredded cheese
Cover with aluminum foil and bake in oven for 20 minutes. Remove foil and continue to bake for 30-35 minutes more, or until the potatoes are tender and the top is golden brown.