Brown the bones in a roasting tray in the oven, turning from time to time. When lightly browned, dot the tomato purée over them and continue browning for a further 10 minutes. Drain the bones of any fat and transfer them to a large saucepan, then add the water and bring to the boil. Once the stock comes to the boil, lower the heat and skim – a lot of fat and scum will have risen to the surface. Allow to simmer for 5 minutes, skimming as necessary. Add the vegetables and the herbs, pour in the white wine and continue to simmer gently for 6 hours.
After 6 hours, strain the stock through muslin or a fine strainer. If there is more than 1.2litres/2pints of stock, reduce it over a high heat until only this amount remains. If you do not do this, the finished stock will not have sufficient strength.
Without a good base stock, a finished sauce can never be a good one, and the one thing that a good stock needs is time. Many people only simmer their veal stock for a couple of hours; I much prefer to cook it for at least 6 hours. It is not until after 6 hours that the bones will have given up all their flavour.