Coarsely grate the potatoes with a box grater. Soak the potatoes and onion in cold water for 5 minutes, then drain well in a colander.
Spread the grated potatoes and onion on a clean tea towel. Twist the towel tightly to wring out as much liquid as possible. Transfer the potato mixture to a large bowl and stir in the egg, parsley, salt, and pepper.
In a large nonstick skillet, heat ¼ cup of the oil over medium-high heat. Spoon the potato mixture into the skillet in 4 places, using about 2 tablespoons mixture per latke, and spread them into 3-inch rounds with a fork. Cook for 2 to 3 minutes, until brown. Turn
the latkes over and cook for an additional 2 to 3 minutes, until the second side is brown. Transfer to paper towels to drain and season with salt. Repeat with the remaining potato mixture, using additional oil as necessary. Serve.
