Cut two bacon strips in half, wash with cold water, and bake at 425 degrees on a baking sheet for 7-8 minutes. Remove from oven, flip each strip over, and bake another 7-8 minutes until crispy.
For the Mornay sauce
In a small saucepan, melt butter over medium heat. Whisk in flour for 30 seconds until absorbed, then whisk in milk.
Bring saucepan to a boil, whisk to blend, then bring heat back to a simmer. Let it simmer for 5-6 minutes.
Slowly whisk in shredded cheeses until smooth, then add nutmeg, salt and pepper. Whisk for another 30 seconds until completely blended.
To build the sandwich
Cut the deli French roll in half length-wise, and then slice each half into another length-wise half. You should have four slices of bread, each the original length of the roll.
On a broiler-safe dish, lay two slices side-by-side. The dish should preferably be an individual size, and should be able to accommodate extra sauce at the bottom without spilling out once it is baking. Small dishes with about an inch-high wall would be ideal for this.
On top of your bread, lay two halves of bacon (1 strip total, cut in half). Top the bacon with layers of turkey, totaling 1/4 pound (or less if you prefer). Spoon 3/4 cup of your sauce onto the turkey, top with two more halves of bacon (1 strip total again), and then finish with two fresh slices of tomato.
Grate fresh Parmesan on top of the tomato, and broil for about 5 minutes, until the cheese sauce is bubbly and Parmesan starts to brown.
Serve hot -but be careful not to touch the dishes with you bare hands!
Notes
The recipe for the Mornay [cheese] sauce makes a little more than 3/4 cup per sandwich. Feel free to lessen it if you wish, or use a different melting cheese if you are not a fan of gruyere. Using any type of bread for this dish is fine; I used the deli roll because I can buy them one at a time and that works better for me!