Tortilla Española

Slice the potatoes 3–4 mm thick (a mandoline helps for consistency). Slice the onion thinly.

Pour the olive oil into a 22–24 cm non-stick skillet over medium-low heat (around 130°C if you have a thermometer). Add the potatoes and onion with a pinch of salt. Cook, stirring occasionally, for 25–30 minutes until the potatoes are completely tender and a knife meets no resistance. They should not brown.

Drain the potato-onion mixture through a sieve set over a bowl — reserve the oil. Let cool 5 minutes.

Beat the eggs in a large bowl with the remaining salt. Add the drained potato and onion and fold together. Rest for 10 minutes.

Return 2 tbsp of the reserved oil to the skillet over medium-high heat. Pour in the egg-potato mixture and immediately reduce to medium. Shake the pan to settle. Cook until the edges are set and only the centre trembles, about 5–6 minutes.

Slide a spatula around the edges. Place a flat plate (wider than the pan) on top. Flip the pan and plate together in one firm motion so the tortilla lands on the plate. Slide it back into the pan, uncooked side down.

Cook for 3–4 more minutes for a runny centre, or 5–6 for fully set. Slide onto a board. Rest 5 minutes before slicing into wedges.