1Cook 8 slices of bacon until crisp - set aside.
In a large skillet, melt 1/2 cup butter over medium heat. Stir in enough flour (5-6 tablespoons or more) to absorb all of the butter. Slowly whisk in the milk, and 8 tablespoons of Parmesan cheese. Stir in the egg to thicken the sauce, but do not allow to boil. Remove from heat, and season with salt and pepper to taste. Heat remaining 2 tablespoons of butter in a small skillet. Saute mushrooms in the butter until soft. Set aside. Preheat your oven's broiler. For each Hot Brown, place two slices of toast onto a heatproof plate or dish. Cover the toast with about 1/4 cup sautéed mushrooms. Place a liberal amount of turkey onto each Hot Brown, and pour an even more liberal amount of sauce over. Smother it. Sprinkle 1 tablespoon Parmesan cheese over the top and a couple of tomato slices. Repeat for each hot brown. Place the entire dish under the broiler until the sauce is speckled brown and bubbly. Remove from broiler, criss-cross two slices of bacon on top.