Heat oven to 350° F. Arrange fillets in a single layer in a large, shallow, buttered baking dish. Add about 1/4 to 1/2-inch of warm water to the dish. Bake for 20 minutes, or until fish flakes easily with a fork.
Prepare Mornay Sauce while fish cooks.
With a slotted spoon, move fish to an ovenproof serving platter. Pour sauce
over fish. Turn oven temperature to broil. Broil fish about 4 inches from
heat for 3 minutes, or until lightly browned.