Submitted by: rick from Milwaukee, Wi
With a whisk, blend all the ingredients (except the lamb) until emulsified.
Place the lamb in a large, plastic brining bag, or some other large air tight container. Pour the marinade over the lamb, and seal. Refrigerate over night.
Preheat oven to 425 degrees. Place lamb, fat side up, on a raised roasting rack with a drip pan beneath, and cook the lamb at 425 for 20 minutes, then reduce the heat to 350 degrees.
Continue to cook for roughly 1 - 1.5 hours (about 12 minutes a pound). Use a meat thermometer to check the meat about every 30-40 minutes, inserting deep into the meat, but not touching the bone. For medium/medium rare, pull the meat out when the internal temperature reads 130-135 degrees. Let the meat rest for 10 minutes before carving, the internal temp will rise to 140.
You can save the marinade for basting the lamb. Bring it to a boil in a stock pot before using a brush or spoon to baste the meat in the last 30-45 minutes of cooking. You can also add vegetables to the drip pan. Potatoes, carrots and onions are great choices. Keep in mind these veggies will cook much faster than the lamb. Add them close to the end, you can let them finish cooking while the meat is resting.