To cook the oxtail
Heat the oil in a wide pan. Brown the oxtail in batches for approx. 5 mins. per batch, remove from the pan, set aside. Add the vegetables, fry for approx. 5 mins., stirring occasionally. Pour in the water, return the oxtail to the pan, bring to the boil. Reduce to a low heat and cook at just below the boil for approx. 4 hrs. If necessary, add a little more water to ensure that the bones remain just covered at all times. Skim off any foam using a slotted spoon. Remove the oxtail, allow to cool slightly.
Pull apart the oxtail with a fork. Heat the oil in a pan. Sauté the onion, garlic and rosemary for approx. 3 mins. Add the meat and tomato puree, cook for a further 2 mins., pour in the wine, reduce almost completely. Pour in the stock, reduce almost completely, season and leave to cool.
To shape the ravioli
Roll out the dough, cut out 40 circles using a cutter or a glass (approx. 8 cm in diameter). Place a walnut-sized portion of filling in the centre of 20 circles, brush the edges with egg white. Place the remaining circles neatly on top, press the edges down firmly, pressing out any trapped air.
To cook the ravioli
Cook the ravioli in batches in just-boiling salted water for approx. 5 mins., drain. Mix the ravioli with the oil, sprinkle the parmesan on top.