1. Bone and butterfly the lamb: Semiboneless lamb has a large bone running diagonally through it, visible at top; sometimes there are two bones. Feel to locate the bottom of bone, then begin cutting at top of bone, cutting down as close to the bone as possible. Go down one side on the sides and bottom, and down the other side of the bone, scraping the meat away so the bone can be removed. You should be able to pull the bone out. Discard or use for lamb broth.
2. Lay the meat out on a cutting board. There will be a larger side and a smaller side. Cut a 45-degree angle into each side and spread out the meat. It will be fairly thick in the middle and thinner at the ends.
3. Whisk together vinegar and oil. In a large roasting pan, pour half the marinade and lay the lamb on top. In a small bowl, stir together coriander, cumin, cloves, cinnamon, pepper, and paprika. Sprinkle seasonings on lamb and rub firmly into the meat. Cut about 10 slits in the meat and insert garlic slices. Pour the rest of marinade on top. Sprinkle herbs over the top of the lamb. Cover pan and marinate in refrigerator for 18 to 24 hours, spooning marinade over lamb once or twice during that period.
4. When ready to cook the lamb, preheat oven to 350 degrees F. Remove lamb from fridge and let sit at room temperature for 15 to 30 minutes. Roast lamb until a meat thermometer inserted in the center registers 135 degrees F to 140 degrees F for rare or 150 degrees F for medium, about 45 minutes for medium. It's very important to use a meat thermometer here so that you don't end up with underdone or overdone lamb.
5. Let lamb rest on a platter or cutting board for 30 minutes. Pour all liquid from roasting pan into a glass measuring cup. Skim off and discard fat. Return juices to pan and add chicken broth. Bring to a simmer over medium heat, scraping any bits from the pan - this is called deglazing. Add salt. Boil until reduced to 3/4 cup. Remove from heat.
6. To serve, slice lamb at a diagonal against the grain. Top each serving with a tablespoon of pan juices.
Source: Hannaford fresh Magazine, March - April 2015