Tortilla Española: The Great Onion Debate, Settled

Peel the potatoes and slice them 3–4 mm thick — a mandoline is ideal but a sharp knife works. Halve the onion and slice into thin half-moons. You want both to be uniformly thin so they cook at the same rate.

Pour the olive oil into a 24–26 cm non-stick or well-seasoned skillet and set over medium-low heat. Add the potatoes and onion. Season with 1 tsp salt and stir to coat. The oil should come about halfway up the potato layers — adjust if needed.

Cook the potatoes and onion in the oil for 22–25 minutes, stirring and turning occasionally, until the potatoes are completely tender when pierced with a knife and the onion is soft and golden. The oil should shimmer gently — if it's spitting or the potato edges are crisping, lower the heat. No browning: that's frying, not confiting.

Tip everything into a colander set over a bowl. Press gently to drain. Let it drain for 3–4 minutes; excess oil in the egg mixture prevents the tortilla from setting properly. Reserve the drained oil — it's fragrant and excellent for future cooking.

Crack the eggs into a large bowl. Add ½ tsp salt and beat well. Add the drained potato and onion mixture and fold together gently. Leave to rest for 5–10 minutes so the potato absorbs some egg.

Heat 2 tbsp of the reserved oil in the same skillet over medium heat until it shimmers. Pour in the egg-potato mixture and level the top with a spatula. Reduce the heat to medium-low.

Cook for 6–8 minutes until the edges are set and pulling away from the sides, and the underside is golden. Shake the pan — the centre should still wobble noticeably. If there is no wobble, it's already overcooked.

Place a large, flat, rimless plate or pot lid firmly over the skillet. Invert in one fast, decisive motion. The tortilla should land browned-side up on the plate. Slide it back into the pan, uncooked side down.

Cook the second side for 3–4 minutes until golden. The centre should still have a slight wobble when you shake the pan — 'cuajada pero jugosa'. Pull it just before you think it's ready; carryover heat will finish it.

Slide the tortilla onto a plate and rest for at least 5 minutes before cutting. Serve at room temperature, cut into wedges as a tapa, or slice thickly and tuck into crusty bread for a bocadillo.