1 boned but untied leg of lamb (about 5pounds after boning)
Combine 1 tablespoon of the crushed peppercorns, the rosemary, mint, garlic, vinegar, soy sauce, and red wine in a large shallow bowl. Add the lamb and turn to coat with the marinade. Marinate the lamb, covered, in the refrigerator, for 8 hours, turning occasionally.
Preheat the oven to 350°F.
Remove the roast from the marinade and drain; reserve the marinade. Roll the roast, tying it with kitchen twine.
Spread the mustard over the meat and pat 2 tablespoons of crushed peppercorns into the mustard. Set the roast in a shallow roasting pan just large enough to hold it comfortably and pour the reserved marinade carefully around but not over the roast.
Bake for 1½ hours, or 18 minutes per pound, basting occasionally. The roast will be medium rare. Bake for another 10 to 15 minutes for well-done meat. Let the roast stand for 20 minutes before carving. Serve the pan juices in a gravy boat along with the lamb.