-
1
For Sauce: In a saucepan melt two tablespoons of butter over moderate heat and cook the onions until soft and golden brown.
-
2
In a heavy saucepan melt the remaining butter over moderate heat, whisk in the flour, and cook the roux, whisking, for 3 minutes.
-
3
Add the milk in a stream, continuing to whisk while bringing the sauce to a boil for 1 minute.
-
4
Season with salt and pepper and reduce heat to low.
-
5
Cook 15 minutes stirring constantly.
-
6
In a large buttered baking dish, at least 2 1/2-inches deep, spread a little of the white sauce over the bottom of the dish and then arrange potato slices in a single layer, slightly overlapping.
-
7
Spread the onions over the potatoes and top with the celery root.
-
8
Spread more sauce over the celery root and sprinkle with the Cheddar.
-
9
Arrange the ham slices and continue to layer the remaining sauce, potatoes, onions, celery root, ham, Cheddar in the same manner ending with a layer of potatoes and sauce on top.
-
10
Sprinkle the top with the remaining bread crumbs and Cheddar and cover with aluminum foil.
-
11
Bake in a preheated 400 Degree oven for 20 minutes.
-
12
Remove foil and continue to bake for 30-35 minutes more, or until the potatoes are tender and the top is golden brown.