In a large oven-safe pot or Dutch oven, heat the olive oil over medium-high heat. Add the chopped onion, garlic, carrots, and celery, stirring until tender—about 5-7 minutes.

Push the vegetables to the side and add the oxtails. Brown them on all sides, about 8-10 minutes.

Stir in the diced tomatoes, tomato paste, Worcestershire sauce, and beef broth. Add bay leaves, salt, and pepper to taste.

Bring the mixture to a gentle boil, cover, and transfer to a preheated oven at 300°F (150°C).

Let it simmer for 3 to 4 hours, until the oxtails are tender and falling off the bone.

Remove from the oven, discard bay leaves, garnish with fresh parsley, and serve hot.