Method

1. Preheat oven to 180°C/ 350°F.
2. In a small sauce pan, melt butter over medium to low heat. Stir in flour until it forms a roux. Cook for 1 minute without coloring, then whisk in the milk a little at a time. Continue stirring until sauce thickens, for about 5 minutes. Season with salt, pepper, nutmeg and the gruyere cheese. Set aside.
3. Slice the buns in half and toast in a pan until slightly golden, take out a set aside. In the same pan, fry the bacon until lightly crisp.
4. Slice rolls in half and spread Dijon mustard over each half. Place in to a baking dish. Top each with 2 slices of chicken mortadella and 1 slice beef bacon.
5. Pour cheese sauce over top and sprinkle with remaining gruyere cheese. Bake for 10-15 minutes until hot and golden brown on top. Sprinkle with parsley and serve.