Preheat the broiler. Cook the bacon in a skillet over medium-high heat until crisp, then drain on paper towels.
Meanwhile, make the cheese sauce: Melt the butter in a saucepan over medium-low heat. Add the flour and stir with a wooden spoon to make a thick roux. Add the milk and bring to a simmer. Cook, stirring, until the sauce thickens, about 5 minutes. Stir in the parmesan, reduce the heat to low and whisk in the egg until the sauce is thick (do not boil). Remove from the heat and season with salt and pepper.
For each Hot Brown, place 2 bread slices side by side in a small flameproof baking dish. Cover the bread with about 1/4 pound turkey and place 1 or 2 tomato slices alongside. Pour 1/2 to 3/4 cup cheese sauce over the turkey and bread. Sprinkle with more parmesan and broil until the sauce is bubbly and speckled brown, 2 to 3 minutes. Remove from the broiler, cross 2 strips of bacon on top and sprinkle with parsley and more parmesan. Serve immediately.