Using a meat mallet, pound veal pieces into 1/4-inch thick, round-ish pieces about 6 to 8 inches across. Lay a slice of prosciutto over each piece of veal and place 2 sage leaves on one half of each slice. Fold each piece of veal in half to form a half moon-shaped "sandwich" and secure with a toothpick. Season each with salt and pepper and dredge in flour. Shake to remove excess flour. In a 12-inch saute pan, heat oil until smoking. Place veal in pan and cook until golden brown on one side, about 4 to 5 minutes. Remove veal pieces from pan and set aside. Add the onion and cook until translucent and soft, about 3 to 4 minutes. Add wine and stock and bring to a boil. Return veal pieces to pan, brown side up. Cook until wine is reduced to 1/4 cup. Add remaining olive oil and gently agitate pan until oil and liquids emulsify. Remove veal and place one piece on each of four warmed dinner plates. Add parsley to pan, stir through sauce, season sauce wtih salt and pepper to taste, pour sauce over veal pieces and serve immediately.