Slice the potatoes into 1/4-inch thick strips. Try to keep them uniform for even cooking.
Soak the fries in a bowl of cold water for at least 30 minutes (or up to overnight). This removes excess starch.
Dry the potatoes thoroughly using a clean paper towel or kitchen cloth.
Heat the oil in a deep pot or fryer to 325°F (165°C).
First fry: Cook the fries in batches for 4–5 minutes until soft but not brown. Remove and drain on paper towels.
Increase oil temperature to 375°F (190°C).
Second fry: Return fries to the hot oil in batches and fry for 2–3 minutes until golden brown and crispy.
Drain and season: Place fries on a paper towel–lined baking sheet. Sprinkle immediately with sea salt and optional seasonings.