Using sharp knife, cut meat lengthwise down center through 2/3 of the thickness. Spread the meat open and pound lightly to flatten slightly.
Spread meat with mustard and scatter peppercorns evenly, pressing into meat with hands. Sprinkle with course ground peppercorn blend.
Place sage leaves down the middle and tie meat back together with twine. Sprinkle outside with peppercorn blend and salt. Reshape tenderloin and place seam side down in shallow roasting pan. Slip bay leaves underneath twine.
Roast for 30 to 50 minutes. Let stand for 10 minutes before carving.