Grate the potatoes and onion on the large holes of a box grater into a clean kitchen towel.

Twist the towel tightly and squeeze out as much liquid as you can, about 1 full minute, until the shreds feel dry.

Transfer the mixture to a bowl and stir in the eggs, flour, salt, and pepper until just combined, about 30 seconds.

Heat ¼ inch of oil in a large skillet over medium-high heat. Scoop ¼ cup portions of batter into the pan and flatten slightly. Fry for 3 to 4 minutes per side until deep golden.

Drain on paper towels, then serve right away with sour cream and applesauce.