Do your French fries come out soggy, limp, and insipid? Try our test kitchen trick for frying them twice which is guaranteed to give you fries with a perfectly crispy, golden brown exterior, and a tender interior.
Peel potatoes and square off sides and ends. Cut lengthwise into 1/3-inch-thick slices, then cut into 4-inch x 1/3-inch x 1/3-inch sticks. Place in a large bowl and add cold water to cover by 1 inch; let soak in the refrigerator at least 4 hours or up to 24 hours. Drain potatoes and spread on a clean kitchen towel and dry completely, patting off as much water as possible.
Line 2 baking sheets with a double thickness of paper towels and put a cooling rack on top of each. Heat 2 inches of oil in a heavy stockpot over medium heat to 300 degrees on a deep-fry thermometer. Working in batches and using a spider (a long-handled, fine-mesh skimmer), lower potatoes into oil (the temperature will drop significantly, to about 270 degrees, and slowly climb up again) and stir to separate. Cook just until softened (test one by breaking in half; it should be almost completely cooked through), but not brown, about 3 minutes. Use a spider or slotted spoon to transfer fries to one of the prepared baking sheets to drain, spreading in a single layer. Allow oil to return to 300 degrees between each batch. (The potatoes can be blanched and left to drain on prepared baking sheets for 4 hours in the refrigerator before finishing, replacing the paper towels as necessary.)
Heat oil to 350 degrees. Again, working in batches, add blanched potatoes to oil (the temperature will drop to about 340 degrees) and stir to separate. Cook until golden brown, 4 to 4 1/2 minutes. Use a spider or slotted spoon to transfer to prepared baking sheets to drain (replace paper towels if you are using the same baking sheets as above). Allow oil to return to 350 degrees between each batch. Sprinkle with salt and serve immediately.