Grate the potatoes using the large holes of a box grater or a food processor. Immediately transfer the grated potatoes to a large bowl of cold water to prevent browning.
Drain the potatoes and wrap them in a clean kitchen towel or cheesecloth. Squeeze out as much excess liquid as possible.
Transfer the squeezed potatoes to a large bowl. Add grated onion, eggs, flour, salt, and pepper. Mix well to combine.
Heat about 1/4 inch of vegetable oil in a large skillet over medium heat.
Drop heaping tablespoons of potato mixture into the hot oil, flattening slightly with the back of a spoon.
Fry for 3-4 minutes per side, or until golden brown and crispy.
Transfer cooked pancakes to a paper towel-lined plate to drain excess oil.
Serve hot with applesauce, sour cream, or your favorite toppings.