Season the oxtail generously with salt. In a large pot set over high heat, brown the oxtail in batches.
Remove and set aside. Add the onions, celery and carrots to the same pot and cook until golden and just starting to soften. Add the garlic and herbs and sauté for another minute.
Add the red wine and allow to reduce slightly then pour in the tomatoes and beef stock.
Add the oxtail back to the pot then pour in the stock - enough to cover the meat. Season generously with salt and black pepper.
Bring up to a boil then reduce the heat, cover and simmer gently for 3-4 hours until the oxtails are pull-apart tender. Alternatively, place in the oven at 160ºC/320ºF. Check every 45 minutes if the oxtail needs more stock and top up as needed.Optional: To thicken the sauce, remove the lid and allow to simmer uncovered for the sauce to reduce for 30-45 minutes.
Serve the soft oxtail with mashed potatoes, polenta or rice.
Notes
Tips for cooking oxtail:
Brown the oxtail: As with any stew, start by browning the meat well in a large, deep Dutch oven or pot set over medium-high heat. This allows the meat to caramelize (Maillard Reaction), adding incredible depth to the stew. Once the meat is browned, remove from the pan and set aside. You can also brown the meat in a large skillet but be sure to deglaze the pan and pour the reduced liquid into the stew to add all that rich flavor.
Add flavor: Using classic aromatics like onion, carrot, celery, garlic, rosemary and bay leaf along with the wine, you're guaranteed an oxtail stew that is packed with flavor. Feel free to play around with herbs like parsley and thyme or add vegetables like mushrooms, zucchini, pumpkin or potato towards the end of the cooking time.
Thicken the sauce: The sauce should reduce and thicken naturally as the oxtails cook but if the meat is tender and you want a thicker sauce, simply mix a few teaspoons of cornstarch with water and stir into the stew. Allow to simmer until thickened.