Warm cream and milk in the microwave for 2 minutes, and set aside.
In a medium saucepan, melt butter over medium-low heat. Stir in flour and cook for 2-3 minutes, stirring continually.
Slowly stir in warm cream and milk, stirring constantly.
Stick 2 cloves into the onion and add to sauce, along with nutmeg and the bay leaf. Simmer for 10 minutes.
Remove onion from the sauce. Pour sauce through a cheesecloth or fine mesh sieve to remove any loose clove particles.
Stir in cheese until melted. Season to taste.
Preheat oven to 400 degrees. Lay bacon in a single layer in a large baking sheet. Cook for 20 minutes, or until crispy. Remove from oven and set aside.
Place tomato slices on a baking sheet. Drizzle with oil, and season with salt and pepper. Place on top rack in oven and turn broiler onto high. Broil 2-3 minutes, until lightly charred.
Arrange bread in a large baking dish. Place a piece of turkey on each bread slice. Pour mornay sauce over each sandwich, fully covering the bread and turkey. Sprinkle with Parmesan.Broil for 2-3 minutes, or until the cheese is melted and golden brown.
Transfer sandwich to serving plates and garnish each with 2 tomato slices, and 2 slices of bacon. Garnish with chives, if desired.