Preheat oven to 375° F.
In a large saucepan or Dutch oven, bring 4 quarts of water to a boil. Add cauliflower. Boil until cauliflower is cooked tender-crisp, about 9 minutes. Drain, refresh with cold water. Drain again.
Prepare bechamel sauce. In a medium saucepan, heat milk to a boil. Remove from heat and set aside. Melt butter in a heavy-bottomed, large saucepan on medium heat. Add flour and stir for about 2 minutes (do not brown).
Remove from heat. Add hot milk in a thin stream, whisking constantly. Increase heat to medium-high. Bring to a boil, stirring constantly. Boil gently for 1 minute, stirring constantly. Remove from heat and stir in 1/2 cup cheese. Add salt and white pepper to taste. Add nutmeg and stir.
Pour 1/3 of sauce in a 12-inch oval gratin pan or an 11 x 7-inch baking dish. Add drained cauliflower in a single layer. Season cauliflower with salt and pepper. Pour remaining sauce over top. Sprinkle with bread crumbs and cheese. Cut remaining butter into small pieces and place sporadically on top of cheese. Gratin can be covered and refrigerated at this point for several hours.
Bake in a preheated oven for 30 minutes. If you want a browner, crisper top, place under broiler, watching carefully to prevent burning. Serve immediately.
Makes: 6