1Season the oxtail pieces with salt and freshly ground black pepper on both sides.
2Heat a pot over high heat with a generous splash of extra virgin olive oil and sear the oxtail pieces until golden brown on all sides.
3Remove the seared meat and set aside. In the same pot, add the chopped garlic, onion, carrot, and leek. Season with salt and pepper and cook until well caramelized.
4Add the tomato wedges to the pot, deglazing the bottom, and continue cooking for another 30 minutes.
5Pour in the red wine and let it cook for 5 minutes to reduce the alcohol.
6Place the oxtail back in the pot, add water to cover the meat, cover the pot, and simmer on low heat for three hours.
7Remove the tender meat from the pot. Separate the solids from the cooking liquid (broth) by straining or discarding the vegetables.
8Boil the remaining broth to reduce for 10 minutes.
9Stir in the butter until incorporated, then add the cornstarch diluted with a little water to thicken the sauce.
10Return the oxtail pieces to the sauce and simmer for a final two minutes.