Into the inner pan of a double-pan cooker put a good ounce of butter; shred a large lettuce and a large Spanish onion and about half a pint of green peas; put all together in the butter, cover the pan closely, and cook for one hour. Strain through a sieve. Make a sauce with the juice, as above, adding the yolk of an egg beaten in at the last, and a tablespoonful of cream with the proteid food.