Remove the beef to a plate, reduce the heat to low and add a little more oil to the casserole, followed by the onion, carrot and celery, stirring to soften a little for a couple of minutes. Return the beef to the pan, along with any juices on the plate and pour in the beef stock and red wine and tuck in the thyme. Bring up to a simmer then cover with a tight fitting lid and slide into the oven. Allow to cook very slowly for around eight hours. When the beef is ready, it is really very tender – test by trying to tease the meat apart a little with a fork. It should give easily. If not, cook for a little longer.