Finely chop the onion, leek, carrot and celery. Heat the oil in a pan, add the chopped vegetables and let sweat and soften in the fat. Add the lentils and stir, then add the stock. Bring to the boil and simmer until The lentils are very soft (about 40 minutes). Add the chestnuts and simmer for a further 20 minutes or so. Liquidize until smooth, adding water as you need. When you want to serve it, reheat and, at the to table, sprinkle each full bowl of soup with parsley and lace with cream.
From: How To Eat by Nigella Lawson