Turn the slow cooker on. Cut the joint into two pieces. Heat a large frying pan with one tbsp of the oil. Season the meat and sear on all sides. Place in the cooker.
Using the same frying pan heat the remaining oil. Add the onion, season and sauté for 5 minutes. Add the remaining ingredients and mix together.
Pour over the meat and cook for 4 hours on high or 8 hours on low. Do not remove the lid during cooking or it will take longer.
Remove the meat from the cooker. Shred the meat with two forks. Pour any excess off from the sauce and mix with the meat.
Serve the meat on toasted buns with rocket, tomato, peppadews or sliced pickles and red onion slices.
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For top tips on protecting you and your family when preparing raw meat and poultry, visit Food Safety in the Home and view the full Food safety at home video.