Clean 6 large, fresh mushrooms and drop into clean water. Melt ½ spoon butter in a saucepan and add the mushrooms, 1 glass bouillon, and the juice from 1 lemon slice. Bring to a boil, remove the mushrooms, and slice them. Fry 1 spoon flour in 1 spoon butter, dilute with 2 glasses of bouillon, boil for 2 hours, and strain through a fine sieve. Add salt, 1 wineglass sherry, and the mushrooms and the sauce in which they were cooked and bring the sauce to a boil. About 2 spoons sour cream may also be added.