Heat oven to 375ºF.
Bend each rack into a semicircle (meat side in, fat side out) and conjoin by tying together the ends with kitchen twine. The rib ends should be pushed outward to create the look of a crown.
Rub the lamb with the oil. Combine the salt, pepper, garlic, thyme, and coriander, and press the mixture all over the lamb. Place the roast in a Bundt pan with the center of the pan coming up through the middle of the roast.
Roast on the middle rack of the oven until the meat reaches an internal temperature of 130ºF, 30 to 35 minutes, or 8 to 12 minutes per pound. Remove from the oven, transfer the roast to a cooling rack, cover with aluminum foil, and rest for 20 minutes.
While the meat is resting, add the vinegar, mustard, and rosemary to the juices that accumulated in the pan while cooking. Stir to combine. Taste and adjust the seasoning as needed. Cut the string away from the roast and place cooked stuffing, rice, or barley in the center, if desired. Serve the warm sauce with the roast.