1. Preparation
Gather all ingredients: bread, ham, cheese, butter, flour, milk, mustard, and nutmeg.
Grate the cheese, such as Gruyère or Emmental.
Prepare a baking tray lined with parchment paper.
Finely chop or measure out any additional ingredients.
2. Make the Béchamel Sauce
In a saucepan, melt 2 tablespoons of butter over medium heat.
Add 2 tablespoons of flour, whisking continuously for about 2 minutes until golden.
Slowly pour in 1 cup of milk, whisking to remove lumps.
Continue to cook until the sauce thickens, about 5 minutes.
Season with salt, pepper, and a pinch of nutmeg. Remove from heat.
3. Assemble the Sandwiches
Take two slices of bread and spread a thin layer of mustard on one side of each slice.
Layer ham and grated cheese generously on one slice, then top with the second slice of bread, mustard side down.
Repeat for additional sandwiches if desired.
4. Cook the Croque Monsieur
Preheat a skillet over medium heat and melt 1 tablespoon of butter.
Place the sandwich in the skillet and cook for about 3-4 minutes until golden brown.
Flip the sandwich, adding another tablespoon of butter if necessary, and cook for another 3-4 minutes.
Once browned on both sides, remove the sandwich and place it on the prepared baking tray.
5. Add Béchamel and Cheese
Spread a generous layer of béchamel sauce on top of the sandwich.
Sprinkle additional grated cheese on top of the béchamel.
6. Finish in the Oven
Preheat your oven to 400°F (200°C).
Place the tray in the oven and bake for 5-10 minutes, until the cheese is bubbly and golden.
Remove from the oven and let cool for a minute before slicing.