01 - Grate the peeled potatoes using a box grater or food processor; grate onion if using.
02 - Place grated potatoes and onion in a clean kitchen towel and squeeze out as much moisture as possible.
03 - Transfer dried potatoes to a large bowl and toss with salt and black pepper.
04 - Heat 2 tablespoons of vegetable oil in a large non-stick or cast-iron skillet over medium-high heat.
05 - Add potatoes in an even 1.25 cm (1/2 inch) thick layer and press gently with a spatula; cook undisturbed for 5 to 7 minutes until golden and crisp underneath.
06 - Flip hash browns in sections or whole using a spatula or plate; add remaining oil and cook for another 5 to 7 minutes until golden and crisp on the second side.
07 - Transfer hash browns to a paper towel-lined plate to drain excess oil; serve hot.