mashed potato, cooked lentils or steamed veg, to serve
In a bowl, mix the flour with a generous grind of black pepper. Place a large, flameproof casserole pot over a high heat and add the oil.
Pat the oxtail dry with a little kitchen paper. Roll the pieces in the seasoned flour and add to the pot one by one. Don’t overcrowd the pan, or you won’t get a good colour on the meat – do it in two batches if necessary. Brown the oxtail on all sides, turning with tongs, until the meat has a nice colour. Remove from the pan and set aside on a plate.
Preheat the oven to 160°C (325°F/Gas 3). Add an extra drop of oil to the pot, reduce the heat and add the onion, carrot and celery. Fry for 4–6 minutes until just tender. Stir through the tomato purée, mustard powder and Worcestershire sauce until evenly combined.
Pour over the red wine, beef stock and balsamic vinegar and pop in the rosemary and thyme sprigs. Season with sea salt. Cover with a lid and place in the oven to cook slowly for 3½ hours until the meat is just about falling away from the bone.
Serve the braised oxtail and its sauce over mash or lentils, or with some steamed veggies.