Begin by gently pounding the chicken cutlets between two sheets of plastic wrap until they're about ¼ inch thick. Season both sides with salt and freshly ground black pepper.

Lay each cutlet flat and place a slice of prosciutto on top, trimming if necessary to fit. Place a sage leaf in the center of each prosciutto-covered cutlet. Secure the layers with a toothpick, pushing it through all layers to hold everything in place.

In a large skillet, heat the olive oil over medium-high heat until it shimmers but doesn't smoke. A drop of water should sizzle when it hits the pan.

Place the cutlets in the pan, prosciutto-side down. Cook for 3-4 minutes until the prosciutto is crispy and golden brown. Carefully flip the cutlets and cook for another 3-4 minutes, or until the chicken is cooked through (internal temperature should reach 165°F/74°C).

Remove the cutlets to a warm plate and tent with foil. If using cornstarch, whisk it with 2 tablespoons of the cold chicken broth until smooth. Add the remaining broth to the pan, scraping up any browned bits. If using, add the cornstarch mixture and cook, stirring constantly, until the sauce thickens slightly, about 2-3 minutes.

Remove the toothpicks, place the cutlets on warm plates, and spoon the sauce over them. Serve immediately while hot.