First of all prepare the vegetables.
The leeks should be trimmed, leaving as much green as possible, then halved lengthways, chopped and washed in plenty of cold water. Then scoop them into a colander to drain. Next peel the carrots and cut them into smallish pieces – and the same goes for the onion. Now take a large saucepan, heat the dripping and add all the prepared vegetables along with the crushed garlic. Stir them around a bit, then cover and ‘sweat’ them for 10 minutes over a low heat, shaking the pan from time to time.
Next pour in the stock, add some seasoning, bring to simmering point, cover and simmer very gently for about 10 minutes, or until the pieces of carrot are tender. Now either sieve or liquidise the soup, then return it to the pan. Taste to check the seasoning, add a few drops of Worcestershire sauce and reheat gently. If you happen to have some Parmesan cheese handy, a little would be very nice sprinkled on each serving.