French Croque Monsieur

Instructions

1. Prepare the béchamel sauce
   In a medium saucepan over medium heat, melt 2 tablespoons of butter. Add the flour and whisk continuously for 2-3 minutes until it forms a smooth paste (roux) that's pale in color. Gradually add the warm milk, whisking constantly to prevent lumps. Continue cooking and whisking until the sauce thickens, about 3-5 minutes. Add the nutmeg, salt, and pepper. Remove from heat and set aside.
2. Assemble the sandwiches
   Preheat your oven to 400°F (200°C). Lightly butter one side of each bread slice. Spread a thin layer of Dijon mustard on the non-buttered side of 4 bread slices. Top each with 2 ounces of ham and 1/4 cup of grated Gruyère. Place the remaining bread slices on top, buttered side up.
3. Toast the sandwiches
   Heat a large skillet over medium heat. Place the sandwiches in the skillet and cook until the bottom is golden brown, about 3 minutes. Flip and cook the other side until golden brown, about 3 minutes more. Transfer the sandwiches to a baking sheet.
4. Add béchamel and cheese topping
   Spread a generous layer of béchamel sauce over the top of each sandwich, spreading it all the way to the edges. Sprinkle the remaining Gruyère cheese evenly over the béchamel sauce.
5. Bake to perfection
   Place the baking sheet in the preheated oven and bake until the cheese is melted and bubbly with golden brown spots, about 5-7 minutes. For extra color, you can broil for the last 1-2 minutes, watching carefully to prevent burning.
6. Serve hot
   Remove from the oven and let cool for 2 minutes before serving. Cut each sandwich in half diagonally and serve immediately on warm plates. Traditionally served with a small side salad dressed with a light vinaigrette to balance the richness.