If the turkey cutlets you have purchased are thicker than 1/4-inch, place each cutlet between pieces of plastic wrap and pound until a uniform thickness of between 1/8 and 1/4-inch is achieved. Season each cutlet on both sides lightly with salt and pepper. Cut the prosciutto slices so that they are of similar size as the cutlets and lay 1 slice of prosciutto on top of each turkey cutlet. Place 1 large sage leaf in the center of each cutlet on top of the prosciutto and secure using toothpicks.
Heat 1 large nonstick skillet over high heat and melt 3 tablespoons of the butter. When hot, add half of the turkey cutlets, sage and prosciutto sides down, and cook until golden, 1 to 1 1/2 minutes. Turn the cutlets to the second side and continue to cook until lightly golden on the second side and just cooked through, 1 to 1 1/2 minutes longer. Transfer the cutlets to a serving platter and repeat with 3 tablespoons butter and cutlets. Set aside. Add the wine to the skillet and cook until reduced by half, 1 to 2 minutes. Finish the sauce with another 2 tablespoons of butter and cook until just melted. Serve the cutlets immediately, with some of the reduced pan drippings drizzled over the top.