This recipe from Millennium Cookbook calls for baking at 300 degrees F. I think I would bake it at 325 or 350 degrees F. but keep an eye on it.

HAM AND CHEESE BAKE

18 slices white bread, crustless
1 cup cheddar cheese, shredded
Chopped or thinly sliced ham
8 eggs
1 1/2 teaspoons mustard
1 cup evaporated milk
2 cups milk
butter (for dotting top of casserole)
2 cups crushed cornflakes or Special K cereal

In a 9x13-inch greased baking dish, layer bread to cover bottom, cheese, ham and another layer of bread.

Mix eggs, mustard, evaporated milk and milk. Pour over casserole. Cover and refrigerate overnight.

IN THE MORNING:
Preheat oven to 300 degrees F.

Dot the casserole generously with butter and sprinkle with 2 cups crushed cornflakes of Special K cereal.

Bake for 1 hour. Let stand 5 minutes and cut into squares.