Cut peeled potatoes into uniform 1/4-inch by 1/4-inch matchsticks using a chef knife or mandoline.

Submerge potato sticks in a bowl of ice water for 30 minutes to remove excess surface starch and prevent oxidation.

Drain the potatoes and pat them completely dry using lint-free kitchen towels; moisture will cause oil splatter and prevent crisping.

Heat oil in a heavy-bottomed pot or deep fryer to a temperature of 325°F (163°C).

Perform the first fry (blanching) by cooking the potatoes in batches for 3 to 5 minutes until they are soft and pale but not browned.

Remove potatoes with a slotted spoon and drain on a wire rack set over a baking sheet; allow to cool to room temperature for at least 15 minutes.

Increase the oil temperature to 375°F (190°C).

Perform the second fry by cooking the blanched potatoes in batches for 2 to 3 minutes until they achieve a deep golden brown color and crisp texture.

Transfer the fries to a paper-lined bowl and immediately toss with sea salt while the surface oil is still hot to ensure adherence.