Spanish omelette

Slice the onion thin into quarter moons. Slice the potatoes thin but not paper-thin, skins on if waxy; quarter big ones first.

Traditional: put the onions in olive oil to submerge, then bring the heat to medium and fry gently until sweet, without browning, for a 5-minute head start.

Lower in the potatoes a few at a time with a spoon and fry gently 10 to 15 minutes, stirring now and then.

Crack the eggs into a big mixing bowl and beat well.

Done when everything has a little colour and some potatoes start to break apart; the onions get about 20 minutes in all.

Strain through a sieve set over a heat-proof jug, keeping the oil.

Put the hot fillings straight into the eggs and stir immediately and aggressively for a couple of minutes so the eggs start cooking without curdling. Add the salt.

Pour into the non-stick pan on medium heat, then turn immediately to low and cook gently four or five minutes until two-thirds to three-quarters cooked inside.

Loosen the edge, put a plate over the pan and flip; slide the omelette back in and cook the second side on medium for colour.

Turn out once more onto a clean plate so the hotter side can steam out; let it rest well before eating.

Variation (modernized): cook two medium onions in a normal coating of olive oil on medium, stirring almost constantly, for a 5-minute head start; add a pound of sliced potatoes and keep stirring about 20 minutes until they break apart, adding a little water if the onions brown too fast.

Variation (modernized): stir the hot fillings into six beaten eggs for a few minutes, add a teaspoon of kosher salt, cook on low or medium-low four or five minutes, flip, and finish on medium; let it cool thoroughly.