Heat the oil in a large pot over high heat. When the oil is very hot (375ºF), add the potatoes slowly, separating the slices with a spoon, and fry for 2 minutes. Reduce the heat to 350ºF, or medium, and fry for 3 minutes, stirring to keep the slices separated and frying evenly. Remove the slices to a basket and shake the excess oil back into the pot and turn off the heat. Spread the potato slices on a baking sheet and allow them to cool for about 10 minutes.
Turn the heat up to high under the oil. When the oil is very hot (375ºF), add the potatoes and fry for 1 minute. Reduce the heat to 350ºF, or medium, and fry until crisp and golden brown, for about 6 minutes. Remove the potatoes with a slotted spoon and drain on paper towels. Sprinkle with the vinegar and salt and serve.
Yield: 6 cups