Fill a large bowl with ice water. Line a large plate or baking sheet with paper towels.
Peel the potatoes then grate them on the large hole of a box grater. Immediately transfer the shredded potatoes to the ice water.
Line a large baking sheet with paper towels. Drain the potatoes then place them in a kitchen towel and squeeze out as much liquid as possible. Scatter the potatoes on the baking sheet, patting them as dry as possible.
Transfer the shredded potatoes to a large bowl then add 1/2 teaspoon salt and 1/2 teaspoon pepper, tossing to combine.
Add the vegetable oil to a large nonstick or cast-iron skillet set over medium-high heat.
Add the potato mixture to the pan, spreading it out into an even layer.
Cook the hash browns, undisturbed, until they begin to turn dark golden brown, about 20 minutes.
Using a wooden spoon or rubber spatula, break the mixture up into pieces, add the butter and continue cooking, stirring intermittently until crisped all over, about 20 minutes.
Transfer the hash browns to a paper towel-lined plate, immediately season with salt and pepper and serve.