Croque Monsieur

Instructions

1. Prepare the béchamel sauce
   In a medium saucepan over medium heat, melt 3 tablespoons of butter. Add the flour and whisk continuously for 2-3 minutes until it forms a smooth paste (roux) that's slightly golden. Gradually whisk in the warm milk, stirring constantly to prevent lumps. Cook for 5-7 minutes until the sauce thickens. Season with salt, pepper, and nutmeg, then stir in the Dijon mustard. Remove from heat and set aside.
2. Assemble the sandwiches
   Lightly butter one side of each bread slice. Place 4 slices butter-side down on a work surface. Spread a thin layer of béchamel sauce on the unbuttered side of these slices. Top each with 2 slices of ham and about 2 tablespoons of grated Gruyère cheese. Cover with the remaining bread slices, butter-side up.
3. Toast the sandwiches
   Heat a large skillet or griddle over medium heat. Cook the sandwiches for about 3 minutes on each side until golden brown and the cheese begins to melt. Transfer to a baking sheet.
4. Add the topping and broil
   Spread the remaining béchamel sauce evenly over the top of each sandwich. Sprinkle with the remaining Gruyère and the Parmesan cheese. Place under a preheated broiler for 3-4 minutes, until the cheese is bubbly and golden brown. Watch carefully to prevent burning.
5. Serve
   Remove from the broiler and let rest for 2 minutes. Cut each sandwich diagonally and serve immediately while hot and cheese is still melty. Traditional accompaniments include a small green salad and French cornichons.