Slice potatoes using a mandolin into 1/4 x 1/8 inch thick fries
soak in cold water for at least 1 hour, and up to 3 hours to remove excess starch
heat several inches of oil in a large cast iron pot or dutch oven until oil reaches 320 F
drain potatoes and pat dry
fry in batches, 2-4 mins until they begin to color and get limp
drain on brown paper lined trays and let cool to room temp
heat oven to 200 F
heat oil to 375 F and fry potatoes again, 2-4 mins until they are golden brown and crisp
do this in batches, returning oil to 375 after each batch
drain fries on brown paper lined tray, sprinkle with sea salt, toss to coat and hold in oven until serving time