Clean and peel the potatoes, then cut them lengthwise into very thin matchsticks. Place the cut potatoes in a large bowl of ice water for 2 to 3 minutes.

Heat the oven to 200°F. Set a wire rack over a rimmed baking sheet for draining and holding the finished fries.

Drain the potatoes and pat them completely dry with clean kitchen towels or paper towels. Work in small batches so the remaining potatoes stay out of the oil until there is room in the pot.

Pour canola or vegetable oil into a heavy-bottomed deep pot to a depth of about 2 inches, leaving plenty of room at the top. Heat the oil to 375°F and check the temperature with a deep-fry thermometer.

Carefully lower a small handful of potatoes into the oil. Fry for about 2 to 4 minutes, moving them gently with a long-handled spider or slotted spoon, until the fries are golden and the bubbling has slowed.

Lift the fries out of the oil and let the excess drain back into the pot. Transfer them to the prepared rack, season with salt, and keep them warm in the 200°F oven while the oil returns to 375°F for the next batch.

Finish with pepper, chile flakes, Parmesan, parsley, malt vinegar, melted cheese, or chili as desired. Serve while the fries are hot and crisp.