Place lamb in a large shallow, no reactive dish.
Combine crushed peppercorns in a small bowl; mixing well.
Set aside 2 tbsp crushed peppercorn mixture.
Combine remaining peppercorn mixture, mint leaves, Burgundy, vinegar, garlic, and rosemary; mixing well.
Pour marinade mixture over lamb.
Cover and marinate in refrigerator for 8 hours or overnight, turning occasionally.
Remove lamb from marinade, reserving marinade.
Roll lamb, tying with heavy string at 2-inch intervals.
Coat lamb with mustard; lightly pat reserved peppercorn mixture into mustard.
Place lamb in a shallow roasting pan; pour reserved marinade around lamb.
Insert meat thermometer into thickest part of lamb.
Bake in a preheated 350 degrees oven for 2 hours and 15 minutes or until meat thermometer registers 160 degrees basting occasionally with pan juices.
Let stand for 20 minutes before slicing.
Serve with pan juices.
Ready in 3 hours.