Peel the potatoes and rinse them under cold water.
Grate the potatoes using a box grater or food processor.
Soak the grated potatoes in cold water for 10 minutes.
Drain the potatoes and pat them dry thoroughly.
If using, finely chop the onion and mix with the potatoes.
Heat the vegetable oil in a large skillet over medium-high heat.
Add the grated potato mixture to the skillet and press down gently.
Cook for about 5-7 minutes until the bottom is golden brown.
Carefully flip the hash browns and cook the other side for another 5-7 minutes.
Season with salt and pepper before serving.