Season the oxtail with salt and pepper generously.
Heat the oil in a 28cm or 11" frying pan or skillet (not nonstick) and when hot, fry the oxtail to get a nice colour on all sides.Remove and place in a saucepan with a 3.5 litre (3 quart) capacity.
Roughly chop the onion, carrot and celery into a 1-2cm (½-¾") dice.
Add the vegetables to the pan that we seared the oxtail in and cook for 5 minutes, scraping the bottom of the pan occasionally.
Pour in the Worcestershire sauce and reduce to almost nothing, stirring occasionally.
Pour in the red wine and reduce by half, stirring occasionally.
Stir in the tomato ketchup and then pour over the oxtail.
Pour over the beef stock, and add in the bay leaves, thyme, and peppercorns.Simmer on low for 3-4 hours. After 10 minutes, have a taste and add salt as required.
When the soup has simmered and the beef is tender, strain the soup.Separate the oxtail from the vegetables and discard the veggies. Cover the liquid and meat in separate bowls, then cool.When cool, refrigerate overnight.
Around 20 minutes before you are ready to serve, skim any fatty deposits from the top of the soup. Your soup should be set like a jelly!Remove around two-thirds of the cloudy sediment.Gently warm the remaining jellified broth over a medium heat.
Pull the meat from the bone and then shred it with your fingers.
When the broth is hot and liquid, remove around 125ml (half a cup) and add it to the flour. Whisk to form a smooth slurry.
Pour into the soup whilst whisking, cook for 5 to 10 minutes, stirring occasionally.
Add in the shredded beef and allow to gently warm through for 4 or 5 minutes.