Ingredients

For the Béchamel

• 2 tbsp unsalted butter

• 2 tbsp all purpose flour

• 1 cup milk

• 1/4 tsp salt

• 1/8 to 1/4 tsp ground white pepper, or to taste

• 1/8 to 1/4 tsp ground nutmeg (optional)

For the Sandwich

• 2 slices white bread

• 1 tablespoon clarified butter, or softened unsalted butter, more to taste

• 2 teaspoons Dijon mustard, more to taste

• 1/2 cup grated Gruyère cheese, or a combination of Gruyère and Emmental

• 1/2 cup béchamel sauce

• 2 to 3 slices ham

• Cooking spray

Directions

Make the Béchamel

1. Gather the ingredients.

2. Heat milk in a small saucepan on the stove or in a glass measuring cup in the microwave until hot but not boiling.

3. Meanwhile, melt butter in a saucepan or saucier over medium heat.

4. Add flour to the pan with the butter-flour mixture and whisk until mixture is well blended. Cook, whisking constantly, for 2 minutes.

5. Gradually whisk in hot milk. Cook over medium heat, whisking constantly, until sauce begins to boil and thicken, about 1 minute.

6. Reduce heat to very low, and simmer, whisking frequently until sauce is smooth and thickened, about 5 minutes.

7. Season with salt and pepper to taste and add a little nutmeg, if desired.

Make the Sandwich

1. Gather the ingredients. Position a rack 6 to 8 inches from the broiler and set the oven to broil.

2. Trim the crusts off of the bread, making the slices as square as possible.

3. Spread both slices of bread with butter.

4. Flip bread over and spread them lightly with Dijon mustard.

5. In a bowl, combine the cheese and half of the béchamel sauce, and mix until the cheese is fully coated.

6. Spread half the cheese mixture evenly onto one slice of bread (on the mustard side, not the butter side). Lay the sliced ham atop the other slice.

7. Press both halves of the sandwich together.

8. Spray a bit of cooking spray onto the surface of a nonstick pan. Heat the pan over medium heat until the oil is hot and glistening but not quite smoking.

9. Place the sandwich into the pan and cook for about 2 minutes, or until the bottom of the bread is a nice shade of golden-brown.

10. Use a nonstick spatula to flip the croque-monsieur over. Lower the heat a bit and cover the pan. Cook for another minute or two, or until the second slice of bread is also golden brown, and the cheese inside the croque-monsieur is fully melted.

11. Transfer the sandwich to a cutting board. Top with the remaining cheese mixture, then spoon the other half of the béchamel over the top.

12. Place sandwich on a sheet tray and broil the sandwich, béchamel-side up, until the top of the sandwich is nicely browned, 1 to 3 minutes. Serve right away.