Heat the oven to 160°C/gas 3. Put the celery, onion, carrots, bay and thyme spring in a casserole dish, with the oil and butter.
Cook until all the ingredients are softened (it should take around 10 minutes). Stir in the flour, followed by the tomato purée, Worcestershire sauce and beef stock.
Gradually stir in 600ml hot water, then add the beef and bring to a gentle simmer. Cover and put in the oven for 2½ hours, then uncover and cook for 30 minutes to an hour more. The meat should be really tender, and the sauce thick. Serve with potatoes or rice.