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Leek and Potato Soup
1 bunch leeks 2 1/2 cups potatoes 1 cup celery 2 tablespoons butter 2 1/2 tablespoons butter 2 tablespoons flour 1 quart milk Salt and pepper Cayenne Cut leeks and celery in very thin slices crosswise and cook in two and one-half tablespoons butter, stirring constantly, ten minutes. Add milk, and cook in double boiler forty minutes. Cut potatoes in slices and cut slices in small pieces; then cook in boiling salted water ten minutes. Melt two tablespoons butter, add flour, milk with vegetables and potatoes. Cook until potatoes are soft, and season with salt, pepper, and cayenne.
A plain white soup built on a milk base rather than stock, in the New England manner. The two butter quantities in the list are not a duplication: 2 1/2 tablespoons sweat the leeks and celery, 2 tablespoons go into the roux.
- Do not let the leeks colourTen minutes of constant stirring in butter is meant to soften them without browning. Keep the heat low; any colour turns the finished soup grey-beige instead of pale ivory.
- "1 bunch leeks"An unquantified market measure. Three medium leeks, white and pale green only, is a reasonable reading against 2 1/2 cups of potato.
- The double boilerForty minutes of milk over indirect heat is insurance against scorching, which was a real risk on a coal range. A heavy-bottomed pan over low heat, stirred often, can substitute, though it will need watching and may want less time.
- Order of assemblyThe instruction compresses several steps: cook the flour in the melted butter a minute or two, then whisk in the hot infused milk gradually before returning the vegetables and drained potatoes. Adding everything at once to raw roux gives lumps.
- PotatoesTen minutes of boiling only part-cooks them; they finish in the milk. Use a floury variety if you want the soup to thicken further on its own, waxy if you want the pieces to hold shape.
- CayenneA period habit in cream soups, used at a few grains rather than a pinch. It sharpens the milk without reading as heat.
- YieldA quart of milk plus the vegetables makes something over six cups, or four to six servings as a first course.
- ReheatingMilk-thickened soups split if boiled after standing. Warm gently and stir; do not bring back to a rolling boil.
Leeks, potatoes and milk make a long-standing cheap-soup combination in northern Europe, though potatoes only became common there from the late eighteenth century. The pairing was in American cookbooks well before Louis Diat popularised a chilled cream version as vichyssoise at the Ritz-Carlton in New York, which he dated to around 1917 and which became widely known in the 1920s and 1930s. The technique here -- butter-sweated aromatics, an infusion in milk held over water, and a separate butter-and-flour thickening -- is the familiar cooking-school method for cream soups, taught with only the vegetable changing from one recipe to the next. The double boiler and the caution against scorching suit an era of coal and wood ranges, where a pan of milk left over direct heat could be ruined quickly.