Peel the potatoes and cut them into 1 cm thick sticks.
Put them in a bowl with cold water and soak for at least 30 minutes to remove the remaining starch from the potatoes.
Transfer the potatoes to a colander and rinse throughly with cold water.
Drain the fries and pat the dry with a paper towel.
In a large bowl add the oil and heat to 150C (300F).
Fry the fries for 5-6 minutes until lightly browned.
Drain with a paper towel.
Increase the heat to 180C (356F).
Fry the fries again for 2-3 minutes until they become crisp.
Drain on a paper towel.
Season fries with sea salt and serve immediately.
