Peel and wash the russet potatoes.
Grate the potatoes into a large bowl.
If using, finely chop the onion and add to the potatoes.
Rinse the grated potatoes under cold water to remove excess starch.
Drain thoroughly and pat dry with paper towels.
Heat the vegetable oil in a skillet over medium heat.
Add the grated potato mixture to the skillet in an even layer.
Season with salt and pepper.
Cook for about 5-7 minutes until golden brown on the bottom.
Flip the hash browns carefully and cook for another 5-7 minutes until crispy.
Remove from skillet and drain on paper towels. Serve hot.