Place a large roasting tray in the oven to preheat.
Remove the hot tray from the oven, then add the oxtail. Season and drizzle over a lug of olive oil, then toss to coat and place in the hot oven for around 20 minutes, or until golden and caramelized.
Meanwhile, trim and halve the leeks, onions, garlic and celery lengthways, then chop into rough 2cm chunks.
Peel and chop the carrots into 2cm pieces, then place into a large ovenproof casserole pan over a medium-high heat with 1 tablespoon of olive oil and fry for around 20 minutes, or until soft and starting to caramelise, stirring often.
Roughly chop and add the thyme and rosemary leaves, then add the bay leaves.
Meanwhile, remove the oxtail from the oven and set aside.
Add the cloves and flour to the veg, stirring well to combine, then pour in the tomatoes and beer or wine.
Add the oxtail and any roasting juices, cover with the beef stock and stir well.
Bring to boil on stove top, then pop the lid on and reduce heat to a good simmer for around 2.5 hours, or until the meat falls away from the bone, stirring every hour or so and adding a splash of water to loosen, if needed.
Strip the meat from the bones and return to the pan, discarding the bones.
Add a good splash of Worcestershire sauce, season to taste and enjoy with creamy mash (celeriac mash goes well).
