1. Combine the potatoes and the oil in a large Dutch oven or heavy-bottomed pot. Cook over high heat until oil has reached a rolling boil, about 5 minutes. Continue to cook, without stirring, until potatoes are limp but exteriors are beginning to firm, about 15 minutes. Meanwhile, line a baking sheet with a double layer of paper towels.
2. Using tongs, stir potatoes, gently scraping up any that stick, and continue to cook, stirring occasionally, until golden and crisp, 5 to 10 minutes longer. Using a skimmer or slotted spoon, transfer fries to paper towel-lined baking sheet. Season with salt (and pepper, if desired) and serve immediately.
Note: Do not use sweet potatoes or russet potatoes; the starch content won't hold up to frying in this manner.