• Preheat the oven to 400 degrees with oven rack in the center of the oven.

Sauce:

• Melt the butter over low heat in a small saucepan. Add the flour and whisk, cooking for about 2 minutes until a tan colored roux is formed. Slowly pour the milk into the roux and whisk constantly until the sauce has thickened, about 4-5 minutes. (If it seems super thick you may add a touch more milk and cook it in for a couple of minutes). Remove from heat and add salt, pepper, pinch of nutmeg, 1/2 cup shredded gruyere and the parmesan and whisk until smooth. Set aside.

Sandwich:

• To toast the bread, place the slices on a parchment lined baking sheet and bake for 5 minutes. Turn each slice and bake for another 2-3 minutes until toasted. Remove from oven.
• Lightly brush half of the bread slices with dijon mustard. Add slices of ham to the dijon coated toasts. Pile most of the remaining gruyere cheese across each ham covered toast. Top the sandwich with other pieces of bread. Slather tops of the sandwiches with the cheese sauce, then top with the remaining gruyere cheese.
• Bake the sandwiches for 5 minutes. Turn on the broiler and broil for about 3 minutes until the top is bubbly and slightly browned.
• Transfer each sandwich to a plate to serve. (If you are having "Croque Madame" then top each sandwich with a cooked over-easy egg.)
  
• Enjoy!