01 - Grate the peeled potatoes using 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 - Warm vegetable oil in a large nonstick skillet over medium-high heat.
04 - Scoop about ¼ cup of mixture per hash brown into the skillet, flatten gently with a spatula, and cook in batches to avoid overcrowding.
05 - Fry each side for 3 to 4 minutes until golden brown and crispy. Transfer to a paper towel-lined plate to drain excess oil.
06 - Continue frying remaining mixture, adding oil as needed. Serve hot.