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Swiss Potato Soup
4 small potatoes 1/2 onion 1 large flat white turnip 4 tablespoons butter 3 cups boiling water 1/3 cup flour 1 quart scalded milk 1 1/2 teaspoons salt 1/8 teaspoon pepper Wash, pare, and cut potatoes in halves. Wash, pare, and cut turnips in one-quarter inch slices. Parboil together ten minutes, drain, add onion cut in slices, and three cups boiling water. Cook until vegetables are soft; drain, reserving the water to add to vegetables after rubbing them through a sieve. Add milk, reheat, and bind with butter and flour cooked together. Season with salt and pepper.
A plain vegetable purée soup thickened with a roux at the end rather than the start. The parboil-and-drain step is the part that matters most.
- Why parboil and drainTurnip loses much of its sulphurous bite in the first ten minutes of water, which is then discarded. Skip it and the soup tastes sharply of turnip rather than of potato.
- The second cooking water is the stockAfter the vegetables are soft, save that liquid. It carries most of the flavour and is what loosens the sieved purée back to soup consistency.
- Sieve or blenderRubbing through a sieve gives a fine, slightly starchy purée. A food mill or a few pulses of an immersion blender does the same; a high-speed blender run long can turn potato gluey, so keep it brief.
- Butter and flour proportionFour tablespoons butter to 1/3 cup flour is a fairly stiff roux for this quantity of liquid. Cook it two or three minutes over low heat until it smells nutty but has not coloured, then whisk it into the hot soup in pieces.
- Scalded milkScalding milk was likely a matter of keeping unpasteurised milk sound and of shortening cooking time. With modern milk it mainly prevents the soup from cooling when the quart goes in; heating it to steaming is enough, and do not let it boil hard.
- Turnip size"One large flat white turnip" means the squat white variety; the recipe gives no weight. Rutabaga is not the same thing and will make the soup sweeter and yellow.
- YieldAbout seven cups finished soup, serving four to six as a first course. It thickens noticeably as it stands; thin with the reserved vegetable water or a little more milk.