Mix together the mustard seeds and remaining ingredients up to the rosemary. Coat the meat with the mixture, cover and leave to marinate in the fridge for about 12 hours. Remove the meat from the fridge approx. 1 hr. prior to frying.
Pre-heat the oven to 220°C. Heat a casserole dish in the lower half of the oven for approx. 5 mins. Salt the meat, transfer to the casserole dish and cook for about 20 mins. Turn oven down to 100°C. Insert the meat thermometer in the thickest part so that it does not touch the bone, cook for about another 2 hours. The core temperature should be around 65°C. Spoon the cooking juices over the meat from time to time. Remove the meat, cover and leave to rest for approx. 10 mins. before carving.