Using your hands, rub the lamb all over with the lemon juice, then pat the garlic and rosemary all over. Season the meat with the salt and pepper and place it in a roasting pan.
Place the lamb in the oven and roast for 30 minutes. Reduce the oven temperature to 350 degrees F and continue to cook for about 1 hour longer for medium-rare, or until a meat thermometer inserted into the center of the roast registers about 145 degrees F to 150 degrees F (be careful that the thermometer does not touch the bone.) Remove lamb from pan and allow to rest for 10 to 15 minutes before carving.
Pour all pan drippings into a sauce pan, scrapping anything into the pan that isn't char. Add fresh herbs and onions to pan, and stir to combine with pan drippings, then add chicken stock and wine. Reduce over high heat until sauce consistency. Strain before serving, if desired. Slice lamb and serve with sauce drizzled over the top.