Grate potatoes and onion, then squeeze out as much liquid as possible in a clean towel.

Mix potatoes with eggs, flour, salt, and pepper until just combined.

Heat oil in a wide skillet to medium-high; a pinch of batter should sizzle immediately on contact.

Fry heaping tablespoons of mixture, flatten gently; cook until deep golden and crackling, about 3-4 minutes per side.

Drain on a wire rack over a tray, sprinkle with extra salt while hot, then serve immediately.