Stew together 400g (15oz) sliced white of leek, 60g (2oz) sliced onion and 100g (3½oz) sliced mushrooms with 75g (2½oz) butter. Moisten with 2½dl (1⅓pt or 3¼U.S. cups) White Bouillon, add 600g (1lb5oz) sliced potato and cook gently. Pass through a fine sieve and adjust the consistency with 3–4dl (10–14fl oz or 1¼–1¾U.S. cups) boiling milk. Pass through a fine strainer, reheat and finish at the last minute with 150g (5oz) butter.
Slices of small white mushrooms well stewed in butter; small dice of potato sautéed and coloured in butter.
This soup may also be prepared as a Cream or a Velouté.