Sarde in Saor — Sardines with Sweet-and-Sour Onions and Raisins

Check the cleaned sardine fillets, remove any remaining bones, and pat the fish dry with paper towels, leaving the skin on. Weigh out 400 g of edible fillets, cover, and refrigerate while you prepare the onions. Cut the onions into thin half-moons and put the raisins in a small bowl with 40 ml of vinegar taken from the 120 ml total. Let them soak for about 20–30 minutes, stirring once; soak them while the onions cook, and do not drain off the vinegar afterward.

Heat 30 ml olive oil in a wide skillet over low heat, add the onions and half the salt, and stir. Cover and cook gently for about 25–30 minutes, stirring every few minutes, until the slices are soft, translucent, and easy to separate with a spatula. Let the onions soften slowly in their own juices without browning deeply; if they start to stick, lower the heat and stir more often. Add the vinegar only once the onions are soft so it does not slow their cooking.

Add the remaining 80 ml vinegar to the soft onions, along with the raisins and their soaking vinegar. Add the pine nuts and cook uncovered over medium-low heat for about 5 minutes, stirring gently, until the raisins soften and a little liquid marinade remains in the pan. Do not let it evaporate completely: it needs to moisten the layers of fish, and the pronounced acidity at this stage is intentional. Transfer the onions and all their liquid to a wide, shallow dish and let cool while you fry the sardines.

Put the flour on a flat plate and take the sardines out of the refrigerator in small batches just before frying. Pour the sunflower oil into a clean, deep-sided skillet about 24 cm in diameter; it should form a layer about 1 cm deep. Heat over medium heat for about 5 minutes, until a pinch of flour sizzles gently right away without darkening rapidly. Lightly coat the first batch of fillets with flour on both sides and shake off the excess so no thick, dry patches remain on the fish.

Carefully lay the fillets in the oil in a single layer with a little space between them, frying all the fish in 3–4 batches. Fry over medium heat for about 2 minutes per side, until the coating is lightly golden and the flesh is opaque and flakes easily with a fork; adjust the heat so the flour does not burn. Transfer the fish to a plate lined with paper towels, sprinkle with the remaining salt, and coat each new batch just before adding it to the oil. When finished, discard the unused flour that has been in contact with raw fish; let the oil left in the skillet cool, then discard it without adding it to the onions.

Once drained, move the sardines off the paper towels onto a wide plate in a single layer and let cool for about 20–30 minutes, until they are no longer steaming. The onions will cool during this time too; do not wait for both components to become completely cold. Spread a thin layer of onions in a shallow glass or ceramic dish, add some of the fish, then continue layering, finishing with onions. Distribute the raisins, pine nuts, and all the liquid from the dish between the layers, lifting the fillets gently without breaking them.

Cover the dish and immediately refrigerate at no more than 4°C for 24 hours. Both the fish and the onions must go into the refrigerator within 2 hours of finishing their own cooking; the brief cooling described here fits within that time. Resting lets the fish absorb the flavor of the marinade and softens the flour coating. Vinegar of a different acidity will give a slightly different flavor, but this marinade does not replace refrigeration and does not preserve the dish at room temperature.

After a day, take the dish out of the refrigerator and gently divide the sardines among four small plates, lifting them with a wide spoon or spatula. Divide the soft onions, raisins, pine nuts, and remaining marinade among the servings. Serve cold, without reheating: the fish coating should now be soft from the marinade, and the onions juicy and sweet-and-sour. Return any leftovers to the refrigerator immediately and eat them by the next day.