Cook leek in 2 teaspoons of the hot oil until tender. Combine leek, nuts, bread crumbs, Parmesan cheese, 2 tablespoons of the fresh sage or 2 teaspoons of the dried sage, and parsley. Set aside.
Remove skin from turkey in 1 piece; set aside. Remove bone; split breast into 2 equal pieces. Place breast halves, skinned sides down, on plastic wrap, so the 2 halves form a square. Cover with plastic wrap. Pound with the flat side of a meat mallet to 1/2-inch thickness. (The breasts should form a rectangle.)
To stuff, arrange prosciutto or ham atop turkey. Spoon stuffing onto prosciutto or ham. Starting with a side that is parallel to the turkey seam, roll up turkey and stuffing. Wrap skin around turkey. Tie with string. Place on a rack in a roasting pan. Brush with remaining oil. Insert a meat thermometer into center. Roast in a 375 degree F. oven for 1-1/4 to 1-1/2 hours or until thermometer registers 170 degrees F. and turkey is no longer pink. Cover; let stand 10 minutes, reserving 2 tablespoons drippings.
Spoon reserved drippings into a medium saucepan. Stir in flour. Stir in broth and wine. Add remaining fresh or dried sage. Cook and stir until thickened and bubbly. Cook and stir 2 minutes more. Serve with turkey. Makes 12 servings.