Trim the leeks and cut off the harder ends — you’ll need about 400 g(14 oz) of trimmed leek. Slice the leeks quite finely and put them in the sink with cold water. Swish them around with your hands to get rid of any dirt. Scoop them up into a colander to drain and wash them again if they are still sandy.
Melt the butter in a fairly large pan. Add the leeks and garlic and sauté over medium–low heat until all the water has evaporated and the leeks are soft and faintly golden. Add the brandy and carry on cooking until it has evaporated. Add the potatoes and season well with salt. Add 1.5 litres(52 fl oz/6 cups) of hot water and bring to the boil. Turn down the heat slightly, cover with a lid and simmer for about 45 minutes, or until the leeks and potatoes are very soft. Grate in a little nutmeg. Purée the soup until it is totally smooth. If it is too thick for your taste, add a little hot water. If it seems too thin, return it to the pan and cook uncovered until it has thickened a bit. Taste for seasoning and add salt if necessary. Add the cream, heat through and serve immediately, with a good tablespoon of parmesan sprinkled over each serve.
Adults should grind pepper over theirs and, ideally, top with a few very fine slices of truffle!