Method

1. Grate the red onion and place in a dish large enough to hold the meat lying flat
2. Next stir in the crushed garlic and olive oil. Add the balsamic vinegar and season with black pepper. Mix everything thoroughly
3. Now place the beef flat in the dish and make sure that the meat is completely coated with the onion and balsamic mixture
4. Cover with clingfilm and marinate for at least 1 hour in the fridge but preferably overnight
5. Remove the meat from the fridge 15 minutes before you are ready to grill it
6. Then place the beef over a hot barbeque and cook for 4 to 5 minutes each side if you want your steak cooked ‘rare’, cook for a minute or two longer for ‘medium’ and leave the steak for 6 to 8 minutes each side if you like your beef ‘well done’
7. When the beef is cooked, leave to sit for about 5 minutes and then slice into 1½ inch strips and serve immediately