2) Turn off the heat and add the salt, pepper, nutmeg, 35g of the grated Gruyere and all the Parmesan. Mix well and set aside.
3) To toast the bread, place the slices on 2 baking sheets and bake for 5 minutes. Turn each slice and bake for another 2 minutes, until toasted.
4) Lightly brush half the toasted slices with mustard, add a slice of ham to each, and sprinkle with half the remaining Gruyere. Top with another piece of toasted bread.
5) Slather the tops of the sandwiches with the cheese sauce, sprinkle with the remaining Gruyere and bake the sandwiches for 5 minutes. Turn on the grill element and grill for 3 to 5 minutes, or until the topping is bubbly and lightly browned. Serve hot.