Bacalao al pil pil

Step 1: Desalt the 4 thick salt cod loins, skin on 24–48 hours before: rinse off the surface salt and put the pieces skin side up in a large bowl of cold water in the fridge. Change the water 3 times a day. After 24 hours, taste a flake from the thickest piece; it should be lightly salted, like fresh fish seasoned. If it's still salty, keep soaking.

Step 2: Drain the cod and pat it very dry with kitchen paper. Leave it to come to room temperature for 20 minutes while you prepare the oil; cold fish chills the oil and slows the sauce.

Step 3: Put the 1 ¼ cups mild olive oil in a wide clay cazuela or a heavy, shallow frying pan just big enough to hold the cod in one layer. Add the 6 cloves garlic and warm over a low heat for 4–5 minutes until pale gold. Add the 1 dried red chilli (guindilla or cayenne) for the last 30 seconds, then lift the garlic and chilli out with a slotted spoon and set aside.

Step 4: Take the pan off the heat and let the oil cool for 5–10 minutes, to about 60–158°F: warm enough to make your hand feel the heat above it, but no longer shimmering. Common mistake: cooking the cod in hot oil. It fries, the gelatine doesn't come out, and the sauce never thickens.

Step 5: Lay the cod in the oil skin side down and return it to the lowest heat. Cook very gently for 5 minutes, so the oil just trembles with small bubbles. You'll see little white drops of gelatine collecting in the oil.

Step 6: Turn the pieces over, skin side up, and cook for 4–5 minutes more, until the flesh is opaque and flakes when pressed, about 145°F/145 °F in the thickest part. Lift the cod onto a warm plate.

Step 7: Pour most of the oil into a jug, leaving about 4 tablespoons with the gelatine juices in the pan. Off the heat, swirl the pan round and round in small circles (or whisk with a small sieve held flat), adding the reserved oil back a thin trickle at a time, until the sauce turns thick, pale and creamy. This takes 8–10 minutes of steady swirling.

Step 8: Return the cod to the pan skin side up, along with any juices from the plate, and swirl gently for 2 minutes over the lowest heat to warm it through and coat it in the sauce.

Step 9: Scatter over the fried garlic, chilli and the 1 tbsp flat-leaf parsley if using, and serve straight from the pan with bread.