Using a paring knife, cut a 7.5cm wide pocket, about 5cm deep, into the side of each tenderloin. Season the cavity with salt and pepper. Stuff one slice of prosciutto, one slice of cheese, and two basil leaves into each pocket. Tie one piece of kitchen twine at each end and one piece in the center of each tenderloin to secure the filling. Season the stuffed tenderloins with salt and pepper.
In a large skillet, heat the oil over medium-high heat, add the tenderloins and sear until golden brown, about three minutes per side. Transfer the tenderloins to an oiled baking pan. Roast for 8 to 10 minutes or until the internal temperature registers 65°C on an instant-read thermometer for medium-rare.
Place the skillet over high heat, add the marsala wine, and cook for one minute, scraping the brown bits that cling to the bottom of the pan with a wooden spoon. Add the chicken stock and cook until the liquid is reduced by half, about four minutes. Remove the frying-pan from the heat and whisk in the butter until melted.
Remove the kitchen twine, slice the tenderloins and arrange on serving plates. Spoon the sauce over the sliced tenderloin and garnish with the cutletped basil.
*Cook's note: This recipe will also work with beef rib spencer steaks or filet mignon.