Rinse veal and pat dry. Pluck leaves from sage and top each cutlet with two leaves.
Cover with a slice of prosciutto and gently pound flat.
Dredge in flour.
Cook in a skillet in hot oil on one side. Turn, cook briefly until pink, then keep warm in an oven preheated to 80°C (approximately 175°F).
Deglaze drippings with Marsala and let reduce slightly.
Remove from the heat and stir in cold butter in pieces. Season with salt and pepper. Arrange cutlets on preheated plates and serve with the sauce.