How to Make It
Season the chicken with salt and pepper. Place 2 sage leaves on each breast. Top with a slice of prosciutto, trimming it to fit. Press the prosciutto to help it adhere to the chicken. Dust the chicken with flour, shaking off the excess.
Heat a large skillet. Add the oil and 2 tablespoons of the butter. Add 2 of the breasts, prosciutto side up, and cook over high heat until nearly cooked through, about 3 minutes. Turn the chicken and cook just until the prosciutto begins to shrink, about 1 minute. Transfer the chicken to a plate; repeat with the remaining chicken. Pour off any fat and wipe out the skillet.
Add the remaining butter to the skillet. Add the wine and cook over high heat until reduced by half, 2 minutes. Add the stock and bring to a boil. Cook until reduced by half, 3 minutes.
Return the chicken to the skillet, prosciutto side up, and simmer over moderate heat until the chicken is cooked through, about 2 minutes; season with salt and pepper. Transfer the chicken to plates, pour the sauce on top and serve.