Pound each halved chicken breast until it reaches a thickness between ½ inch and ¾ inch. Season both sides with salt and pepper, then evenly distribute the tablespoon of minced sage over the chicken. Press one slice of prosciutto onto each piece, covering it completely, then press a fresh sage leaf into the center of each prosciutto slice to adhere. Combine the flour with a pinch of salt and pepper in a shallow dish, dredge each prepared chicken piece lightly in the flour, shaking off excess. Heat the olive oil in a large sauté pan over medium heat, then sear the chicken in batches, starting with the prosciutto side down, for approximately 2½ to 3 minutes per side until golden and cooked through. Remove the cooked chicken and set aside. In the same pan, add the diced shallot and minced garlic, sautéing for 1 to 2 minutes until fragrant. Deglaze the pan with the white wine, cooking until nearly evaporated. Pour in the chicken stock and allow it to simmer over high heat for 3–4 minutes until it reduces to a thin gravy. Whisk in the butter, remaining teaspoon of sage, and minced parsley; adjust seasoning with salt and pepper as needed. Spoon the finished sauce generously over the chicken saltimbocca and serve immediately.