1clean the mushrooms and break off stems. In a large pot, simmer the stems in the beef stock for 35 to 40 minutes. strain the stock through a sieve into a bowl; discard the stems. return the stock to the pot. mix the flour and butter to paste, and roll into balls. bring the stock to a boil; drop the balls into the stck and mix withj a wisk until stock thickens. slice the mushroom caps thinly and add them to the stock. simmer for 10 minutes. meanwhile, beat the evaporated cream in another pan stirring just to the simmering point then stir into the stock. add the sherry and stir in the cream and add salt. reheat the soup until hot and serve on heated soup plates.