Fry the pancetta in a large heavy-based saucepan set over a moderate heat for 5 minutes, until browned. Add the celery, onions, carrot, garlic and 2 Tbsp extra virgin olive oil, cook for 5 minutes, then set aside.
Sear the oxtail pieces in the remaining extra virgin olive oil in batches, until well-browned, then return the vegetable mix, tomato paste, wine stock and tomatoes. Add the herbs and spices, season with salt and pepper, then simmer gently for 3 hours, until tender. Serve with crisp semolina discs and salsa verde.