The amounts above will produce about 5 litres of soup. If you want less, simply half the amounts given.
Trim, chop and wash the leeks.
Easiest way is to agitate the chopped leeks in a large pot of water. Then scoop the leeks out. All the grit will have sunk to the bottom.
Roughly chop the carrots, onions and celery.
Rinse the lentils in cold water till the water is clear. Usually half a dozen times. This cleans them and gets rid of the "dusty" taste.
Put the lentils, carrots, onions, celery and two thirds of the leeks into a big pot. The soup will at least double in bulk. For the amounts given use a 5 Litre pot.
Cover well with water or ham stock, bring to the boil and simmer until the vegetables and lentils are soft. Stir regularly, lentils stick easily.
Whizz till smooth in a blender or with a blender stick.
Finely chop the parsley and remaining leek. Add them to the soup and leave to cook in the residual heat.
If you are making the meat version, add any ham hough you prepared earlier. A lump of butter adds a nice creaminess.
Season to taste.