Croque Monsieur

4 tablespoons butter, melted
2 tablespoons flour
1 1/2 cups milk
1/2 teaspoon salt
1/2 teaspoon freshly ground pepper
1/2 teaspoon fresh ground nutmeg
6 ounces Gruyere cheese, grated (about 1 1/2 cups grated)
1/4 cup grated Parmesan cheese (packed)
4 slices thick-cut French or Italian loaf bread
8 ounces ham, sliced
Dijon mustard

Heat a grill pan to medium high heat. Prepare béchamel sauce by heating 2 tablespoons of butter in a small saucepan until melted. Add flour and whisk together and cook for about 1 minute, continuing to whisk to avoid "burning" the flour. In small portions, add the milk while whisking - a little at a time to "break up" the butter flour combination until it becomes smooth and creamy. When all of the milk has been added and the sauce has thickened, add 1/2 of the Gruyere cheese, parmesan cheese, salt, pepper and nutmeg. Stir together and set aside. Lightly brush all sides of the bread with 2 tablespoons melted butter and place on the grill pan to toast lightly. Remove and carefully spread a coating of the Dijon mustard, a slice of ham and the rest of the cheese on top of the sandwich. Place in a 350°F oven and cook until the cheese is melted. Remove cookie sheet from the oven and increase temperature to broil. Spoon 2-4 tablespoons of the béchamel sauce on top of each sandwich and return to the oven to broil for 1-2 minutes or until it begins to bubble and brown. Remove and let rest before serving. Hint: Use a baking rack over top of the cooking sheet for better results and crunchier bread.