A traditional Spanish fishermen’s recipe made on the beach with any fish too inferior to sell at the market, the name of the dish references the small cauldron, a caldero, used to cook this soupy fish and rice dish. Paella rice is crucial, swelling in the stock but still retaining a chewy bite. Aïoli is a good addition to the finished caldero, all pungent and garlicky.
To make a quick fish stock, put about 400g of fish bones into a saucepan with a peeled clove of garlic, a few fennel and coriander seeds and a few slices of celery and onion. Top up with 850ml of water, then bring to the boil, skimming off any froth that collects. Simmer for about 10 minutes, then strain and put to one side until ready to use.