Peel four good-sized potatoes; cut into very thin slices lengthwise. Cut off the ends, giving them a square appearance. Throw into cold water for half an hour, then drain and dry on a towel. Put a portion into the frying-basket; put them down into the fat at a temperature of 240 Fahr. Shake them until they are half cooked, not brown; drain them; throw them in a pan that has been lined with paper. Continue the frying. When you are ready to serve the potatoes, put a few back into the frying-basket and plunge them down into the very hot fat - about 350 to 360 Fahr. They will at once swell. Drain them in a colander, dust with salt, and continue until you have the desired quantity.