Preheat oven to 250°F. Arrange cubed bread in a large, high-sided sheet pan or roasting pan in a single layer and place in the oven, tossing occasionally, for about 2 hours or until fully dry.
When there's about 30 minutes left on the bread, start the rest of the stuffing components. Mince all of the fresh poultry herbs. Use a fork to mash 1 tablespoon of the minced herbs into 2 tablespoon unsalted butter on a clean cutting board until the butter is quite soft. This is your compound butter.Set aside the rest of the minced herbs for the stuffing. Leave compound butter out to soften until read to use. Melt ½ cup butter in a medium pan over medium heat. Remove the casings from two sausage links and brown them in the pan, using a spatula or wooden spoon to break the meat apart into crumbles. Add the chopped carrots, celery, and onion and cook until the veggies have softened. Set aside (with as much of the buttery pan drippings as you can) until ready to use. When the bread is dry, transfer it to an extremely large mixing bowl along with the sausage mixture and the rest of the minced poultry herbs.Toss everything together until evenly distributed.
Lightly beat two eggs and add them to the bread along with 2 cups chicken stock and salt, stirring well to combine. Set aside to soak while you prep the turkey.
Preheat oven to 375°F with an oven rack in the middle setting.
Pat turkey breasts dry with a paper towel on all sides. Slide a small spatula or your fingers between the skin and the meat to separate it.Season all sides of the turkey generously with salt and pepper making sure you get it between the skin and the meat. Then rub the softened compound butter all over the turkey and under the skin too.
Check the bread. Tear a few pieces apart — if they're still quite dry in the center, add an additional ½ cup-1 cup broth and stir well.
Generously butter a large rectangular casserole dish or baking pan. Arrange the stuffing in an even layer, pressing it down fairly firmly into the pan — just enough to avoid big air pockets without smushing it down flat. To prevent the bottom of the stuffing from browning/burning, you may want to place the casserole dish inside a larger casserole dish. Place your turkey piece or pieces on top of the stuffing and roast until a thermometer inserted into the thickest part of the turkey reads 160°F. NOTE: Depending on your oven and the size of your turkey pieces, this could take anywhere from 1-1½ hours. Start checking on it every 10-15 minutes after it's been in for about an hour. If the turkey is done, remove it from the oven to a cutting board to rest. Give the stuffing a stir, to make sure the bottom and sides aren't browning too much. Return it to the oven until it's browned across the top. If the turkey isn't done after an hour (which is extremely likely, depending on the size!) transfer it to a sheet pan, or, if you had a second casserole dish to insulate the bottom of the stuffing pan, you can place it in that. Continue cooking until the thickest part of the turkey reaches 160F.
Let the finished turkey rest at least 10-15 minutes. Use a sharp knife (like a boning knife) to remove the bone from the bottom of the breast. Slice the turkey and place it back on top of the stuffing to serve.