Pound veal cutlets flat with a meat mullet. Heat butter and oil in a pan and cook sage leaves for about 1 minutes. Remove from pan and pat dry.
Top each cutlet with a piece of proscuitto and a sage leave. Secure with toothpicks. Cook in the same pan for about 2 minutes per side, season wtih salt and pepper.
Remove cutlets from pan and keep warm. Deglaze pan with wine and saute briefly. Arrange veal saltimbocca on plates and drizzle with sauce. Garnish with lemon slices and serve with baguette, if desired.