01 - Grate the peeled potatoes with a box grater or food processor. Transfer to a clean kitchen towel and squeeze out as much moisture as possible.
02 - In a large bowl, mix grated potatoes, chopped onion if using, flour, egg, salt, and pepper until evenly incorporated.
03 - Heat vegetable oil in a large nonstick skillet over medium-high heat until hot.
04 - Scoop ¼ cup portions of the potato mixture into the skillet, flattening gently with a spatula. Fry in batches, avoiding overcrowding.
05 - Fry the hash browns for 3 to 4 minutes on each side, until golden brown and crispy. Transfer to a paper towel-lined plate to drain excess oil.
06 - Repeat with remaining mixture, adding more oil if necessary. Serve hot.