Wash barley, then cook in lightly salted, boiling water for 2 1/2 hours till very soft and gelatinous.

Meanwhile, scrape and chop carrots. Wash and slice celery and leek. Peel and quarter onion. Put all vegetables into a saucepan with bay leaves, salt, peppercorns, parsley, mushrooms and 9fl oz (250ml) water. Cover and simmer gently for 1 hour.

Strain stock into a bowl. Reserve mushrooms and discard remaining vegetables. Slice mushrooms and return to pan with strained stock.

Drain barley and crush with a potato masher, or partly liquidize in a blender. Add barley and vinegar to stock, heat through and season.

Cut butter into small pieces and put in bottom of a warmed soup tureen. Pour in soup, stir in cream and serve.