1. If needed, slice up your remaining turkey breast into 1/4 inch slices, ready for sandwiches. The sliced turkey on the Hot Brown sandwich should be cold when added to the sandwich.
2. Wash & pat turkey necks dry and cut into 2 inch portions. Season with salt and pepper.
3. In a Dutch oven, heat half an inch of oil over medium heat. Cook the turkey necks until they’re nice and dark brown on all sides. Remove and set aside.
4. To the same pot, add the onion, carrot, and celery until they’re cooked down, then add the tomato paste; cook for five minutes, stirring occasionally.
5. Place the necks back into the pot and add the stock and bay leaves, along with the parsley and thyme as well. Bring to a boil, skim the scum that rises with a ladle, and turn the heat to low; braise for two and a half to three hours. Once the meat on the necks is fork-tender, remove the necks and strain the stock into a large container; refrigerate overnight.
6. The next day, pick the neck meat off the bones and make the gravy: In a medium saucepot over medium heat, cook the flour and butter until golden brown, stirring constantly, 10 to 15 minutes. Add four cups turkey stock from the necks.
7. To create the sandwich, place one slice of bread on a plate, then top with three slices of breast and two heaping tablespoons of the cold braised turkey-neck meat, then three more slices of breast. Push down on the meat to compress. Pour hot gravy over the entire sandwich.
8. In a medium saucepan, warm the peas with just a little butter and water; season with salt. Spoon a big pile on top of your hot turkey sandwich.