For Bechamel Sauce

1. Warm the milk in the microwave
2. In a saucepan, melt the butter over medium-low heat
3. When the butter is melted, add the flour and whisk until incorporated and the flour is cooked (about 45 seconds to 1 minute)
4. Add the warm milk and whisk vigorously to avoid lumps
5. Keep whisking until the sauce starts getting thick and creamy.
6. When it boils, remove from heat and add the dijon mustard, 1/4 cup of gruyere cheese, salt, pepper, and nutmeg. Mix until combined
7. Meanwhile, toast the bread slices slightly in the oven or toaster
8. Place the toasted bread slices on a sheet pan or a grill pan
9. Add the ham to 4 of slices of bread
10. Top the ham with grated gruyere cheese
11. Place the remaining bread slices over the gruyere cheese to make the sandwich
12. Top each of the 4 sandwiches with the warm bechamel sauce and extra gruyere cheese
13. Broil for 3-4 minutes or until the top is bubbly and toasted
14. Remove from oven, slice and enjoy!