Croque Monsieur. A delicious toasted ham and cheese sandwich, Croque Monsieur is topped with a bechamel sauce and even more cheese and then broiled to perfection.
Melt butter in small saucepan over medium heat. Whisk in flour and continue to whisk for 1 minute, slowly whisk in milk, salt, pepper and nutmeg. Continue to whisk constantly as the sauce simmers and thickens, about 2 - 4 minutes.
Preheat oven to 450º F.
Assemble sandwiches by spreading a thin layer of whole grain mustard and the sauce on piece of sandwich bread, top with a few ham slices, some Gruyere and Parmesan cheese and another slice of bread. Repeat until all sandwiches are assembled. Brush sandwiches with melted butter.
Place large skillet over medium heat. Place assembled sandwiches into the skillet and toast each side until lightly brown, about 2 minutes each.
Remove the skillet from the stove, spoon more sauce and cheese over top of the toasted sandwiches. Place in the oven until the cheese melts and begins to turn lightly brown, about 2-4 minutes. Remove from the oven and serve immediately.