On the hob heat 2 tbsp olive oil in a large heavy flameproof casserole dish.
Toss the oxtail pieces in the seasoned flour and fry until golden, cooking in batches.
Remove and place on the side.
Heat the remaining oil in the same casserole dish, add the celery, onion and carrots and cook until they begin to soften slightly.
Pour on the beer and allow to bubble through, scraping the base of the pan to deglaze. Reserve this vegetable and beer mixture.
Wipe out the casserole with kitchen paper and layer the oxtail, vegetable and beer mixture, tomatoes, bay leaves and garlic. Season with salt and pepper. If necessary top up with water to cover all the meat.
Bring to a gentle simmer on the hob and cook slowly for 3-3½ hours until the meat comes away from the bones.
Alternatively cook for the same time in preheated oven at 140°C/120°C/Gas 1
Serve with: Potato and celeriac mash and roasted root vegetables.