Mince finely three large white potatoes, also the white part of three medium-sized leeks, fry in one ounce of fresh butter without allowing to colour. Wet well with a pint of light stock made from veal or chicken, or both mixed. Let all cook gently until quite tender, then pass through a fine sieve.

Return to the fire. Boil up again, and add seasoning of salt, one gill of cream, one ounce of fresh butter, well worked in, and add lastly a pluck of chervil.