Place the flour in a large Ziploc bag with the mustard powder and season with salt and pepper. Add the oxtails and close the bag, trapping a little air. Shake the bag until all the pieces of oxtail are evenly coated in the flour mixture, then remove from the bag, shaking off any excess flour.
Heat a large casserole dish big enough to fit all the oxtails with the vegetables that will eventually join them but not so large that, on pouring in the wine, the level has to be bumped up with water to cover the oxtails.
Add the beef dripping to the casserole and brown the oxtails all over in two batches, turning them regularly with tongs.
Carefully wipe out any burnt bits from the bottom of the casserole with some kitchen paper.
Return the oxtails to the casserole with the shallots, celery, garlic, thyme, bay leaves, cloves and nutmeg. Pour over the wine to just cover the oxtails.
Bring to a gentle simmer, skimming off any scum that rises and settles on the top.
Put the lid on, and place the casserole in the oven for 1 1/2 hours, then remove it from the oven.
You will notice that a lot of fat has come out of the oxtail and risen to the top. This needs to be removed. If skimming it when hot, tilt the casserole at an angle and ladle out the fat. Alternatively, leave it to cool down and the fat will become opaque and stiff so it can easily be scraped off.
Once you have removed all of the fat, turn the oxtails over and stir in the swede, parsnips and carrots with the redcurrant jelly and tomato puree. Season with salt and pepper.
Return the lid, and cook for another 1 1/2 hours at the same oven temperature as before.
Remove the casserole from the oven, tilt it and skim off any excess fat. Remove one piece of the oxtail and check that it is cooked by pulling at a meaty piece with a fork.
Garnish with chopped parsley and serve with sourdough bread or mashed potatoes.
