Place beef, onions, balsamic, tomato paste, and bay leaves in a slow cooker or oven proof dish.

For the slow cooker, cover and cook on auto for 10-11 hours or until beef is meltingly tender.

For the oven, add in a cup of water, cover and bake at 120C (250F) for 6-8 hours or until beef is meltingly tender. Add in a little water if the beef starts to dry out.