
Trim any excess fat from the oxtails and toss the meaty pieces in the seasoned flour, patting off and reserving the excess. Heat 2 tablespoons of the oil in a large, flameproof casserole and fry the oxtails in 2 batches until well browned. Remove to a plate.
Add 1 tablespoon of oil, 25g butter and the chopped onion to the casserole cook, stirring, for about 10 minutes until richly browned.
Stir in the remaining flour and cook for 1 minute. Gradually stir in the beef stock, wine and jelly and bring to the boil, stirring. Return the oxtail to the casserole with the garlic
and bouquet garni, and season with salt and plenty of black pepper. Cover and simmer gently for 2.5 hours, turning the meat from time to time, until just tender but not falling apart. Remove the casserole from the heat and leave to cool, then chill overnight in the fridge.
The next day, peel the button onions. Slice the celery and carrots. Slice the leeks and rinse in cold water. Heat the remaining 1 tablespoon of oil in a saucepan. Add the onions and fry for 3 minutes. Add the leeks and cook for a further 3 minutes.
Spoon the fat from the top of the casserole and discard. Gently reheat for 5 minutes, then stir in the vegetables and prunes. Simmer, uncovered, for 30 minutes, or until the vegetables are tender.
Heat the remaining butter in a frying pan, add the breadcrumbs and fry gently for 3 - 4 minutes until crisp and lightly glden. Season and stir in the parsley. Sprinkle on top of the casserole and serve, ideally with lots of mashed potatoes.