Begin by making the cornbread stuffing. Melt half of the butter in a pan over medium heat and toss in the apple cubes. Cook for approximately 2 minutes until apples are a light brown and then set aside in large bowl. In the same pan melt the remaining butter and add the rosemary and sweet Italian sausage. While cooking, break up Italian sausage and cook until lightly browned then add the onions and continue cooking for 10 minutes until soft and golden. Add sausage mixture to the apples in the large mixing bowl along with cornbread pieces, season well with salt and pepper, and give it a good toss until it's well combined. In a separate bowl, whisk together the egg, cream, and stock, and pour that over the cornbread. Stir the stuffing together and set it aside in refrigerator.
Now prepare to butterfly the turkey breast. Use a sharp, thin knife to cut down the length of the turkey breastbone to remove the breast. Cut the breast parallel to the board, almost in half just stopping short of the outside edge. Open out the 2 halves as if you were opening a book. Now you've got a large piece of meat that will cook evenly and is thin enough to roll.
Lay turkey breast flat. Sprinkle the cut surface of the turkey with salt and pepper and then spread out the stuffing Â½ inch away from edge so the breast can be rolled and tied. Start with the left side and roll the turkey over the filling and into a cylinder. Tuck in the ends if you need to contain the stuffing. Then, using 4 pieces of kitchen twine tie turkey in 4 places and season all over with salt and pepper.