There are plenty of reasons why the crown rack of lamb has such a fancy, special-occasion reputation: It's expensive, made from two full racks of lamb ribs; it's too challenging to make for everyday cooking; and it looks spectacular. Ask your butcher to French the bones for you. Frenching is the common trimming technique for crown roasts that gives it a neat appearance. Some butchers will also form it into a circle for you at your request. If you decide to form it yourself, use a helper for the best result.
Rinse the flat racks of lamb and pat dry.
Brush the lamb racks with olive oil on both sides, then sprinkle with salt, pepper, garlic and herbs to taste. Rub the seasoning into the lamb.
Cut a slit in the membrane between each rib with a sharp knife.
Place the two racks in the roasting pan with the bones sticking up. With both hands, form the two racks into a crown shape. Have another person tie the butcher's string around the outside of the roast in two or three places so that it stands on its own.
Preheat the oven to 204 degrees Cahreneheit. Place the roasting pan in the oven, uncovered and cook for 30 minutes.
Remove the roast and use a meat thermometer to take the internal temperature of the meat. It should read 62.8 degrees Celsius for medium rare. If it's below 62.8 degrees Celsius, return it to the oven for five to 10 minutes more.
Let the roast sit for five minutes before transferring it to a serving platter.
If you prefer you meat medium, cook it to an internal temperature of 71.1 degrees Celsius. For well-done, cook it to 76.7 degrees Celsius. If you like, you can put paper frills on the ends of the bones after roasting. You can find frills for crown roasts at speciality kitchen stores. Rare meats are 51.7 degrees Celsius to 57.2 degrees Celsius, but the USDA recommends cooking meats to at least 62.8 degrees Celsius to ensure all food-borne bacteria are killed.
Do not overcook your roast -- it will become tough and dry.