Preheat oven to 425 degrees F.
Cut lamb into 2, 4-rib racks. Trim excess fat and place in a small roasting pan. Roast 10 minutes, and then remove from the oven. Place crumb mixture on a plate. Brush top and sides of lamb with mustard. With a towel, lift up lamb by the ribs and press mustard-coated portions into the crumbs. Place lamb back into the roasting pan and cook to desired degree of doneness. Cook 12-15 minutes more for rare, 15-18 for medium rare, and 20 for medium. Rest the lamb 5 minutes to allow juices to set before serving. If you would like to make jus to serve with the lamb, remove fat from the pan, add 1 cup of beef stock, simmer a few minutes, and then season with salt and pepper.