There are dishes that mirror the entire logic of a region. Papas alinas is an Andalusian tapa from Cadiz with exactly six ingredients: potato, onion, eggs, parsley, olive oil and vinegar. Nothing more. And that is precisely what makes it harder than it looks - when there is no sauce to hide behind, every mistake shows.

The key is not the composition. The key is when you season it. The potato has to be mixed with the vinegar, oil and salt while it is still warm. Warm potato absorbs the liquid; cold potato just carries it on the surface. That is the whole difference between a dish that tastes of something all the way through a mouthful and one that only tastes of something at the bottom of the plate.

The proportions and the method are simple. One kilogram of medium potatoes is washed and put into salted water together with three eggs - in the same pot, so you do not light two burners. Once boiling, the eggs come out after nine to ten minutes and go straight into cold water to stop the cooking. The potatoes carry on for another twenty to twenty-five minutes, or around thirty if they are larger. They are done when a knife goes in without resistance.

While they boil, slice one spring onion or half a sweet onion into thin strips or small cubes. If your onion is too sharp, soak it briefly in water. The parsley is chopped fine, leaves only. When the potato is warm but you can already handle it, peel it and cut it straight over the plate. The eggs are peeled and broken over it, then the onion and parsley go in, then salt, sherry vinegar and olive oil.

Notice what is missing: mayonnaise. None. No sour cream either, no mustard, nothing to blanket the potato. Around here potato salad heads almost automatically in that direction, and this recipe shows there is another route - the one that leans on acidity instead of fat. You feel the difference in heaviness right after lunch.

The only place worth spending a bit more is the vinegar and the oil. When there are six ingredients, two of them carry the entire flavour. Purists insist that adding tinned fish, tomato or pepper ruins the classic recipe - and essentially they are right, though every household ends up adding something of its own. Serve at room temperature, not cold from the fridge.