For the onions:
1/2 pound (1 medium) yellow onion, peeled, halved and sliced into 1/4-inch half-moons
1 small fresh bay leaf
1 tablespoon canola oil
1 tablespoon unsalted butter, cut into 4 cubes
Freshly ground black pepper
For the Mornay sauce:
2 tablespoons unsalted butter
2 tablespoons flour
1/2 teaspoon salt
1/4 teaspoon freshly ground black pepper
A few grates of fresh nutmeg or 1/8 teaspoon ground nutmeg
1 cup warm milk
1 cup grated Gruyere cheese
For the sandwiches:
1/2 cup grated Gruyere cheese
1/2 cup grated fontal cheese
8 slices country bread, about 7 inches across and 1/2-inch thick
4 tablespoons (1/2 stick) unsalted butter, at room temperature
4 teaspoons Dijon-style mustard
1/2 cup caramelized onions
6 ounces Camembert cheese, cut into 1/4-inch-thick slices
8 ounces very thinly sliced Virginia or Black Forest ham (see note)
1 cup Mornay sauce
1. For the onions: Heat a large saute pan over medium heat for several minutes. Spread the onions evenly in the pan, along with the bay leaf, and let them sit untouched for a couple of minutes. Drizzle the oil evenly over them and dot with butter. Do not stir them for several minutes. (The goal is to let some of the onion's moisture evaporate and to get some good color on the onions at the start. Once you stir, water will be released, and the caramelizing will end until that water evaporates.) Stir the onions, using a flat-edged wooden spoon to scrape up all the browned bits from the bottom of the pan. Season to taste with salt and pepper. Let the onions cook, stirring often, for 20 to 25 minutes, until they are golden brown and nicely caramelized. The yield is about 1/2 cup.
2. For the Mornay sauce: Heat the butter in a small saucepan over medium heat until it bubbles. Whisk in the flour, salt, pepper, and nutmeg, and cook for 2 or 3 minutes, to create a nutty-brown roux. Slowly whisk in the milk, beating constantly to prevent lumps from forming. Cook the sauce for 2 or 3 minutes, until well thickened and bubbling. Remove from the heat and add the cheese, stirring until it is melted. The yield is about 11/4 cups.
3. For the sandwiches: Position a rack in the upper third of the oven and preheat the broiler to high. Line a baking sheet with aluminum foil. Combine the Gruyere and fontal cheeses in a small bowl.
4. Completely cover each slice of bread with butter on one side and with mustard on the other side. Place 4 of the slices in a large nonstick skillet, buttered side down. Top each slice with 2 tablespoons of caramelized onions, Camembert slices, ham slices, and 1/4 cup of the grated cheese mixture. Top each with a slice of bread, buttered side up. Cook the sandwiches over medium heat until golden brown, 5 to 7 minutes, lightly pressing down on them with a spatula to ensure even toasting. Carefully turn the sandwiches over and toast them on the second side until golden brown, 4 to 6 minutes.
5. Transfer the sandwiches to the baking sheet and spread about 1/4 cup of Mornay sauce over each one. Broil for 3 or 4 minutes, until the sauce is bubbling and nicely browned. Serve right away.
Note: Deli ham in grocery stores often is loaded with water. It is a good idea to portion the ham for your sandwiches, place the portions on a plate between a double thickness of paper towels, and microwave the ham for 30 seconds. This releases a lot of the water. Blot the ham with the paper towels as much as possible.
Per half-sandwich: 410 calories, 19 grams protein, 25 grams carbohydrates, 6 grams sugar, 26 grams fat, 80 milligrams cholesterol, 950 milligrams sodium, no dietary fiber.