Begin by marinating the beef ribs. In a food processor, combine chopped apple, chopped onion, soy sauce, mirin, garlic, ginger and brown sugar and blitz well. Alternatively, grate apple and onion and combine all other ingredients in a bowl and mix well. Cut the beef short ribs into manageable pieces, about 2-3 inches wide, and add them and the marinade to a zip lock bag. Make sure each piece is well-coated by gently massaging the bag after it has been closed. Cover and refrigerate for at least 5 hours or overnight for the best results.
When you are ready to cook the beef ribs, pre heat a fan forced oven to 150°.
Place beef ribs and marinade in a high lipped baking tray and cover tightly with foil.
Bake at 150° for three hours, then remove from the oven and turn the oven temp up to 180°.
Remove the foil and gently turn each rib once, then place tray back in the oven uncovered for 20 - 30 minutes (keep an eye on them so they don't burn).
Once done, remove from the oven and allow the ribs to rest for 10 - 15 minutes before serving.