Lift an ordinary toasted ham and cheese sandwich to "gourmet" status by making a traditional Croque Madame. Laden with rustic French charm, a classic Croque Madame is essentially a ham and cheese sandwich that's covered in a smooth and creamy bechamel sauce and topped with a gooey egg. Variations of the sandwich include the Croque Monsieur, which omits the egg, and you can opt to make either decadent classic with this simple recipe.
Make a Roux
To create the bechamel sauce, melt 1/4 cup of the unsalted butter in a medium saucepan until it begins to foam. Add the flour and whisk constantly to form a roux -- working until the mixture is combined, thick and pulls away from the sides of the pan.
Add the Liquids
Gradually whisk in the milk, stirring until smooth. Continue to cook until the sauce is thick and elastic, about 4 minutes. Remove from the heat, and then whisk in 1 tablespoon of Dijon mustard and the nutmeg.
Season to taste. Cover the surface directly with plastic wrap, and set aside until needed.
Build the Sandwiches
Heat your oven to 400 F / 200 C.
Arrange 4 slices of the bread on a parchment-lined baking tray, and lightly spread half of a tablespoon of Dijon mustard over each.
Spread each slice of bread with 1 to 2 tablespoons of bechamel sauce.
Add a piece of ham to each slice of bread.
Sprinkle half the cheese on top of the ham.
Top each portion with another slice of bread.
Spread the top of the sandwiches with 1 tablespoon more of the remaining bechamel.
Top With Cheese
Sprinkle the remainder of the cheese over the top, and then season with cracked salt and pepper.
Bake until the sandwiches are golden-crisp and the cheese and bechamel are bubbling away -- about 15 to 20 minutes.
Cook the Eggs
While the sandwiches are baking, heat the remaining butter in a frying pan, and cook the eggs sunny-side-up until their bases are crisp and the whites are set but the yolks are still runny.
When you remove the toasts from the oven, top each with a fried egg.
If you desire a traditional Croque Monsieur (without an egg), simply remove the toasts from the oven and serve immediately.
Accompany this dish with a dash of good quality relish or savory jam, extra Dijon mustard or a small green salad to cut through the richness.