Boil 900g of waxy potatoes in their skins until tender. Drain and rinse in cold water, then peel and slice.
Fry 1 medium chopped onion in a little oil in a large skillet until golden, then set aside.
Add a little more oil and fry the potato slices in a single layer, in batches, turning once, until golden brown on both sides. Season with salt and pepper.
Stir the onion into the last batch for a few seconds, combine with the rest, and season with more salt and pepper.
