Trim fat from the ox tails and cut into sections between the joints.
Peel the carrots and onions, trim the celery and cut into even-sized pieces about. Heat the oil and butter in a frying pan and brown the oxtail well on all sides.
Transfer the meat to a large casserole. Add the vegetables to the pan and toss regularly until they are well browned.
Add the flour and cook for 2 - 3 minutes until flour begins to brown lightly.
Add the plum jam, vinegar, sugar, beef stock, red wine and bouquet garni and stir well to make a smooth mixture. Bring to the boil and then pour over the oxtail.
Cover and cook at 150 C for 3 hours until the meat is very tender and falling off the bone. Taste the sauce and season with salt and pepper if needed.
(Don't forget to remove the bouquet garni.) If possible, leave the casserole to stand overnight to allow the fat to rise and set. Skim off fat and re-heat. Serve with creamy mashed potatoes with chopped parsley.
NOTE:-If the sauce needs to be thicker mix an extra tablespoon of flour with 2 tablespoons butter and stir into the casserole bit by bit 5 minutes before serving.