Lightly pound the chicken breasts to 1/4 inch thick. Season with salt and pepper and lay a sage leaf on each breast. Lay 1 slice prosciutto over each and fold in half like a book. Secure the two sides with a toothpick and dredge whole piece in flour seasoned with salt and pepper. In a 12 inch to 14 inch saute pan, heat oil until just smoking. Add chicken and saute until golden brown on both sides. Add shallots and mushrooms and cook until mushrooms have sweated, about 5 to 6 minutes. Add marsala and chicken stock and cook over high heat until reduced by half. Swirl in