Cook the bacon on a sheet pan in the oven for 15-20 minutes or until crispy. When bacon is done, remove from the sheet pan to a paper towel lined plate.
Melt the butter over medium heat in a 2 quart saucepan.
Once butter is melted, add the flour and stir continuously for 3-4 minutes.
Slowly add the milk, whisking continuously for 5-10 minutes until thickened. While the mornay sauce is thickening, add the sea salt, black pepper, and chives.
Once the sauce has thickened, remove from the heat and whisk in 1/2 cup of parmesan cheese. Set aside.
Preheat the broiler to high.
Place 6 slices of bread on a sheet pan.
Add turkey and tomato slices on top of the bread slices.
Pour the mornay sauce over each, smothering the tomato and turkey.
Sprinkle the second 1/2 cup of parmesan on top of the mornay.
Broil for 3-4 minutes, or until the top of each hot brown is melty and bubbly.