Wash the oxtail pieces and pat dry with kitchen paper. Trim off as much excess fat as possible. Put the flour in a freezer bag and season well with salt and pepper. Put half the oxtail pieces into the seasoned flour, toss well to coat, then put aside on a plate. Repeat with the remaining oxtail pieces.
Heat two tablespoons of the oil in a large non-stick frying pan. Brown the oxtail over a medium heat for about 10 mins, turning every now and then, until dark brown all over. You may need to add extra oil if the pan looks dry at any point. Put the browned oxtail into a flameproof casserole dish.
Return the frying pan to a low heat and add the onions, garlic, carrots and celery. Add a little extra oil if necessary. Cook gently for 10 mins, or until softened and lightly browned, stirring occasionally.
Tip the vegetables on top of the beef and add the thyme and bay leaves. Stir in the wine, beef stock and tomato purée. Season with salt and pepper, put the casserole on the heat and bring to agentle simmer.
Cover the casserole dish with a lid and cook in the centre of the oven for 3 hours. Stir after 1½ hours, turning the oxtail in the sauce.
After 3 hours, the meat should be falling off the bones and the sauce should be thick. Remove the casserole dish from the oven and transfer the oxtail pieces to a plate, set aside and keep warm.
Skim any fat that has pooled on the surface of the sauce.
Divide the oxtail pieces between six warmed plates and spoon over the sauce.
Sprinkle with the chopped parsley (if using) and serve with mountains of creamy mashed potato and fresh vegetables.
Recipe by appetite magazine at https://www.appetitemag.co.uk/oxtail-stew/