01 - Wrap the grated potatoes in a clean kitchen towel and squeeze firmly to extract excess liquid. Transfer to a large mixing bowl.
02 - Add the grated onion, sliced scallions, egg, flour, salt, and pepper to the potatoes. Mix thoroughly until all ingredients are evenly incorporated.
03 - Pour 2 tablespoons of vegetable oil into a large nonstick skillet and warm over medium heat.
04 - Drop 2 to 3 tablespoons of the potato mixture into the hot pan, using a spatula to gently flatten each into a patty approximately 1/2 inch thick.
05 - Cook 3 to 4 potato cakes at a time for 3 to 4 minutes per side, flipping once, until both sides are golden brown and crispy. Add more oil between batches as necessary.
06 - Transfer the finished cakes to a plate lined with paper towels to drain. Keep warm while frying the remaining batches.
07 - Plate the potato cakes hot, topped with a dollop of sour cream and garnished with chopped fresh chives or scallions if desired.