Rinse shredded potatoes until water is clear, then drain and squeeze dry. Place shreds in a bowl, and mix in the onion, flour and egg until evenly distributed.
Heat about 1/4 inch of oil in a large heavy skillet over medium-high heat. When oil is sizzling hot, place potatoes into the pan in a 1/2 inch thick layer. Cover the whole bottom of the pan, or make separate piles like pancakes. Cook until nicely browned on the bottom, then flip over and brown on the other side. It should take at least 5 minutes per side. If you are cooking them in one big piece, it can be cut into quarters for easier flipping.
Remove from pan, and drain on paper towels. Season with salt and pepper and serve immediately.