-
1
Warm a generous film of olive oil in the marmita or a heavy pot over a medium flame. Add the onions with a pinch of salt and cook, stirring occasionally, until completely soft, translucent, and beginning to colour at the edges — the base must be sweet before anything else enters the pot.
-
2
Add the tomatoes and the scraped flesh of the choricero peppers (or the paste). Cook, stirring, until the tomato breaks down and the mixture deepens to an even red-orange and loses its raw smell.
-
3
Pour in the white wine and allow it to reduce by half, then add the broken potato pieces and season with salt. Add enough water or light fish stock to cover the potatoes by approximately 2 cm. Bring to a steady simmer.
-
4
When the potatoes are roughly three-quarters cooked — tender at the edges but still firm at the centre — partially break several pieces against the side of the pot with a spoon. This is the cascar la patata step: the fractured surfaces release starch directly into the broth, building body without flour or roux. The broth should turn visibly cloudy and coat the spoon lightly. This is where the dish lives or dies — potatoes cut cleanly or left whole will not release enough starch, and the broth will remain thin.
-
5
Continue simmering until the potatoes are fully tender and the broth has reached a loose, soup-like consistency — more liquid than a thick stew. Taste and correct the salt at this point; the potato should be well seasoned throughout.
-
6
Add the bonito cubes to the pot, cover immediately, and remove from the heat. Allow the residual heat of the broth to finish the fish for 3–4 minutes. The cubes are done when they are just opaque at the surface but still yielding to gentle pressure — they must not be left long enough to turn firm or chalky.
-
7
Serve at once in the marmita or in deep earthenware bowls, ensuring each portion receives both potato and fish in generous broth.