Mix the marinade ingredients in a bowl.
Coat the beef in the marinade and leave for at least an hour in the fridge (for best results overnight).
Heat the vegetable oil in a heavy bottomed pan and gently sweat the onions until translucent. Then add the beef to the pan and brown on all sides.
Add the chicken stock and bay leaves and bring to the boil.
Transfer into an oven safe casserole dish with a lid and put into a pre-heated oven at 180°C for around 1 hour 30 minutes or until the beef is tender.
Shred the beef just before serving and serve with warm tortillas, sour cream and tomato salsa.
Tip: After step 4, transfer to a slow cooker and put on a low heat for six hours, the meat will be meltingly tender.
