Croque Monsieur: Grilled Ham and Cheese Sandwich

First, prepare the béchamel sauce: In a small saucepan, melt 15g of butter over medium heat. Add the flour and whisk constantly for 1-2 minutes to create a roux. Gradually pour in the cold milk, whisking continuously to prevent lumps, until the sauce thickens. Season with salt, pepper, and nutmeg. Remove from heat and set aside.

Preheat your oven to 200°C. Lightly butter one side of each bread slice with the remaining 10g of butter.

Spread a thin layer of Dijon mustard on the unbuttered side of two bread slices. On these two slices, layer half of the grated Gruyère, then two slices of ham, a spoonful of béchamel, and finally the rest of the ham.

Top each sandwich with the remaining bread slices (buttered side out). Spread a generous layer of béchamel sauce on top of each sandwich and sprinkle with the remaining grated Gruyère.

Place the sandwiches on a baking sheet. Bake in the preheated oven for 10-15 minutes, or until the cheese is melted and bubbly, and the top is golden brown. For an extra crispy top, you can finish it under the grill (broiler) for 1-2 minutes, watching carefully to prevent burning.

Serve immediately, perhaps with a simple green salad. Enjoy your authentic Croque Monsieur, bon appétit!