Croque Monsieur is kind of like the ultimate ham and cheese sandwich. The name loosely translates as "The Crunch Master." It took me a few tries to perfect these, but the recipe I finally landed on goes:
2 slices of white sandwich bread
2 thin slices or 1 thick slice of ham
1 thick slice of Emmental cheese
Béchamel sauce (best served hot)
Begin by melting some butter into a large skillet or a griddle, to coat the surface thoroughly. Place the bread into the buttered pan and let it cook over medium-high heat for 2 minutes or until beginning to brown on one side. Flip the bread slices, and very quickly spread Dijon mustard over the pre-toasted side of one of the bread slices and return it to the pan. Lay the ham on one piece of bread and the cheese on the other, and let the bread cook and toast until the cheese begins to melt and the ham is warm. (You may need to reduce the heat to keep the bread from burning.) When the filling is warm, remove the bread slices from the pan and place them face up on a dish. Pour or spread Béchamel sauce on the ham and the cheese, then close the sandwich. It is now ready to be eaten. Depending how much of the sauce you put in, this sandwich can be messy -- might be best consumed with a knife and fork, or at least with plenty of napkins handy!