- Preheat oven to 170c / 335F
- Mix together the garlic, rosemary sprigs, mustard, orange zest, salt & pepper
- Unravel the defrosted boneless butterflied leg of lamb and spread the above mix inside the lamb. Roll the lamb up again and tie the leg together using the string
- Sprinkle the outside of the lamb generously with salt, pepper & olive oil
- Place the lamb in a roasting pan along with the quartered onion and orange.
- Pour broth around the lamb and cover the pan with foil. Roast for 4.5 hours until tender
- Remove the foil and brown the lamb for 45 minutes or until well browned
- Remove lamb and cover it to rest while making the gravy
- Skim off some fat from the liquid and place on an pan on medium high. When the liquid bubbles add 4 Tablespoons of flour.
- Whisk the flour and cook for 1 min
- Add the rest of the liquid in and reduce until desired thickness
- Add salt and pepper to taste