Preheat oven to 400 degrees F.
Butterfly open turkey breast to 1/2-inch consistent thickness, skin on (or have your butcher do this for you). In a 10-inch to 12-inch saute pan, heat 4 tablespoons butter over medium heat until foam subsides. Add prosciutto, chestnuts, turkey giblets and onion and cook until onion is golden brown, 8 to 10 minutes. Remove from heat and allow to cool. Add cool luganega sausage, grated cheese and eggs and mix well.
Stuff turkey by laying mixture all over flesh and then roll up like a jelly roll. Stuff ham under skin and tie entire roast several times with butcher twine. Place roasting pan just large enough to hold it and rub with sage and rosemary. Pour stock and wine into pan and place in oven. Roast 50 to 70 minutes, or until internal temperature is 165 degrees F. Remove from oven and remove turkey to carving board and allow to rest 10 minutes.
Meanwhile, degrease liquid in pan, preferably with a degreasing cup with a spout starting at the base. Place liquid in a small pan and bring to boil. Knead remaining 2 tablespoons butter with 2 tablespoons flour to form paste and whisk it in, bit by bit, until slightly thickened. Season with salt and pepper. Carve turkey into 3/4-inch slices and serve with sauce and perhaps some Sauteed apples.
Recipe Courtesy of Mario Batali