Season the flour with salt and pepper.
With a meat mallet, pound the chicken breasts to 1/4-inch thickness. Season each breast with salt and pepper and lay 1 sage leaf on each breast. Lay 1 slice prosciutto over each piece and fold in half like a book. Secure the two sides with a toothpick and dredge each breast in the seasoned flour.
In a heavy-bottomed pot with high sides, heat the 2 cups olive oil to 375 degrees. Make sure that you have a slotted spoon or spider close by. Working in a few batches, fry the leaves in the oil, removing with the slotted spoon after 30 seconds. Season with salt, set on a plate lined with paper towels to drain, and set aside.
In a 12 to 14-inch saute pan, heat the remaining olive oil until smoking. Add the chicken and saute until golden brown on both sides. Add the shallots and mushrooms and cook until the mushrooms have sweated, about 5 to 6 minutes. Add the Marsala and chicken stock and cook over high heat until reduce by half. Swirl the butter into the pan, add the parsley and serve on 4 warmed dinner plates, topped with the fried sage leaves.
Recipe copyright 2000, Mario Batali. All Rights Reserved.