Flatten chicken breasts, cut in half, and dust lightly with flour. = Saute in a skillet with oil over moderately high heat for 1 minute on = each side until golden brown. Transfer to a plate, discard oil in = skillet. Add butter and broth into the skillet and heat mixture over = moderate heat. Return chicken to skillet, top each piece with prosciutto = and cheese and cook the mixture, covered, until the cheese is melted and = bubbly. Transfer the chicken to a heated platter, reduce sauce over = moderately high heat until it is thickened and season with salt and = pepper. Pour the sauce over the chicken.