Heat 1 tbsp of the vegetable oil in a casserole and brown the beef, in batches, until golden all over, then remove onto a plate. Add the remaining oil and stir-fry the kimchi, onion, garlic, carrot and mooli for 5 minutes, then add the gochujang and gochugaru, and continue to cook for another 2 minutes. Tip the beef back in, including any juices, top up with 750ml of water and bring to the boil. Put on a lid, turn down to a gentle simmer and cook for 2 hours. Remove the lid, add the mushrooms and cook for another 1 hour until the sauce has reduced slightly and the beef is meltingly tender. Season with the soy sauce and sprinkle with spring onions and sesame seeds. Serve with white rice and extra kimchi, if you like.