Now leeks are in season, for pottage full good,
That spareth the milch cow, and purgeth the blood.
Tusser in his 'Five Hundred Points of Good Husbandrie'
Leek Soup; Take a sheep's head, prepared by having had the hair and wool scalded off and the head split in two, take out the brains, and put the head in three quarts of boiling water, add twelve large leeks, cut up into pieces about two inches long, simmer the whole gently for four hours. Mix smoothly as much flour or ground rice as will make the soup tolerably thick, mix it with the soup, and continue stirring until the whole is well done. Season to taste and serve hot.
Our War-Time Kitchen Garden Tom Jerrold (1917)