Boiling makes the potatoes tender; double-frying makes them insanely crispy.
Cut the potatoes into 1/3-inch-thick steak fries.
Transfer the potatoes to a bowl of cold water.
Bring a large pot of salted water to a boil. Drain the potatoes, add them to the pot and boil just until tender.
Carefully drain the potatoes and transfer them to a paper towel–lined rack to cool. Refrigerate until chilled.
In a large, deep skillet, heat 2 inches of oil to 250° and set a rack over a baking sheet. Working in batches, fry the potatoes just until they begin to brown around the edges, about 8 minutes.
Transfer the potatoes to the rack and let cool. When all of the potatoes have been fried once, heat the oil to 350°.
Fry the potatoes again, in batches, until golden and crisp.
Drain the fries on a paper towel–lined baking sheet.
Sprinkle with salt and serve.