In a large bowl, mix together the grated potatoes and onion. Squeeze out any and all excess moisture using a clean kitchen towel or paper towels.
Add the beaten egg, flour, salt, and black pepper to the bowl and mix well until all ingredients are combined.
Heat the vegetable oil in a large non-stick pan over medium heat. Add the whole mixture to the pan and evenly distribute it throughout.
Cook the hash browns for about 4-6 minutes per side, or until they are golden brown and crispy.
Remove the hash browns from the pan and pat off any excess oil.
Serve the hash browns hot with scallions and enjoy!