Sorropotún Cántabro

Sorropotún is Cantabrian, from San Vicente de la Barquera, and it is bonito and potato cooked like a working harbour knows how to cook it: plain, filling, and exact where it matters. It is close kin to marmitako, yes, but this belongs to Cantabria, with the potato snapped into the pot so its starch thickens the broth around the fish.

The step that decides it is the potato. Don't cut it cleanly all the way through. Cut halfway, then crack it loose with the knife, chascar la patata, so the rough edge gives body to the broth. A neat cube stays polite and separate. A snapped potato helps make the stew.

Use bonito del norte in season if you can, firm and fresh, and add it only at the end. It needs minutes, not punishment. Far from Cantabria, use albacore tuna if it is fresh and good, or a firm tuna steak at a pinch, but know it will be a little leaner and less sweet. No hace falta haber pisado España. You need good fish, a slow sofrito, the onion-and-pepper base, and the sense to stop cooking before the bonito dries out.

In my Margin beside this one I wrote: "fish last." That is the whole warning. Build the broth, cook the potatoes tender, turn off the heat, and let the bonito finish gently in the pot. Siempre sale, si lo sigues.