Croque monsieur, a delicious combination of ham and Gruyère cheese on toasted bread and covered with a béchamel sauce, first appeared on menus in Paris around 1910. Some variations dip the bread in egg before baking it. Often the sandwich is topped with additional cheese on top of the bread to create a melty, cheesy crust. The version that adds a fried egg on top, said to resemble a lady’s hat, is called the croque madame.
I've written more about this decadent sandwich for the Monitor's weekly magazine here.
For quick reference, I've included the recipe below. Enjoy!
Croque monsieur tartine
For the béchamel:
2 tablespoons unsalted butter
2 tablespoons all-purpose flour
1-1/4 cups hot milk
Salt and freshly ground pepper, to taste
Ground nutmeg, to taste
For the tartine:
Four thick slices of country-style bread
8 slices of cooked ham
2/3 cup grated Gruyère cheese
1. Preheat oven to 450 degrees F. Lightly grease a baking sheet with butter and set aside. Grate the cheese.
2. To make the béchamel: Add butter to a heavy-bottomed saucepan and melt over low heat. In a separate small saucepan, heat milk over low heat (do not let it come to a boil).
3. While the milk heats, whisk the flour into the melted butter, stirring constantly, until the mixture smells nutty and fragrant, about 1 minute. Do not let it brown. Slowly add the hot milk to the butter-flour mixture, whisking constantly until the mixture is smooth. Increase the heat to medium, bring to a simmer and season with salt, pepper, and nutmeg. Continue to cook, stirring occasionally, until the sauce is thickened, about 3 minutes more. Remove béchamel from heat.
4. To assemble the tartines: Place the bread slices on the greased baking sheet with two overlapping slices of ham on top. For each sandwich, spread 1 to 2 tablespoons of the béchamel over the ham (more, if desired). Sprinkle grated cheese evenly over the béchamel. Bake until the cheese melts and evenly browns, and the bread is golden and crisp on the bottom, about 12 to 15 minutes.
5. Serve immediately with a simple salad of mixed greens.