Canola or peanut oil, for frying
2 large russet potatoes
(about 1 lb. 10 oz.), peeled
Kosher salt, to taste
1. Pour oil to a depth of 2" into a 6-qt. heavy-bottomed dutch oven and heat over medium-high heat until a deep-fry thermometer registers 375°.
2. Meanwhile, julienne potatoes lengthwise using the narrowest setting of a mandoline with a julienne attachment or by hand with a sharp knife; transfer potatoes to a strainer and rinse them briefly under cold water for 1 minute so that they won't stick together as they fry in the oil. Drain potatoes, transfer to kitchen towels, and pat dry.
3. Working in 4 batches, fry potatoes, stirring constantly with a slotted spoon and maintaining an oil temperature of at least 350° (adding the potatoes will cause the temperature to drop), until potatoes are light golden brown and crisp, about 2 minutes. Using a slotted spoon, transfer fried potatoes to a rack set over a rimmed baking sheet. Season potatoes with salt; serve.