Mary Berry bashes the steak for her beef stir-fry before cooking to tenderise it and then fries it as a piece (rather than in strips) for a more succulent flavour. Make the marinade by placing all ...

In a bowl put the beef. Add the vinegar to the beef and let it tenderise for about 30 minutes. In a pan over medium heat add the oil. Sauté the onions until golden brown, and set them aside.