Beef or Veal Stock au Jus

Makes about 9 pints stock or 1.5 pints jus.. Pre-heat the oven to 110 degrees C/225F. Lay the onion halves flat in a roasting tray with the water. Place in the very cool oven and allow to caramelise slowly until they have totally softened and coloured. This process will take 1-2 hours. The sugars in the onions will slowly cook and give a wonderful taste. Put the onions into a very large pot. Increase the oven temperature to 200 degrees C/400F. Place all the bones and trimmings in a roasting tray and roast for about 30 minutes until well coloured. Roast the chopped carrots and celery in another roasting tray for about 20 minutes until lightly coloured. When ready, add the bones, trimmings and vegetables to the onions in the pot along with the leeks, tomatoes, garlic, bay leaf and thyme. Fill the pot with cold water - you'll need about 9 pints. Bring the stock to the simmer and skim off any impurities. Allow to cook for 6-8 hours - with this you will achieve the maximum taste. When ready, drain and discard the bones and vegetables. This is now your veal/beef stock and you can cool it and freeze it in convenient quantities. Alternatively, you can make a jus from the stock. Allow the liquid to boil and reduce down to about 1.5 pints, skimming occasionally. The stock should now be thick and of a sauce consistency. Make sure that you taste all the time during reduction. If the sauce tastes right but is not thick enough, thicken it lightly with cornflour (cornstarch?) mixed with water. You now have a classic jus to which you can add the juices from your roast, if you wish (after skimming off the fat).