Heat olive oil in a large casserole dish and brown the oxtail pieces over high heat.
Remove meat and cook chopped vegetables for 5 minutes before adding herbs, peppercorns, and tomato purée.
Deglaze with 300ml red wine and simmer for a few minutes.
Return oxtail to the pan, add 1.5l beef stock, and simmer covered for 2.5 to 3 hours.
Transfer meat to a plate to cool and strain the cooking liquid into a bowl.
Shred the meat, discard bones, and refrigerate both meat and liquid separately overnight.
Remove the solidified fat from the liquid and heat the remaining stock in a pan.
Mix 1 tbsp flour with 3 tbsp hot soup and whisk back into the pan to simmer for 2 minutes.
Stir in the shredded meat and heat through before serving.