A northern Peruvian causa rooted in coastal tradition. Yellow potato enriched with salted mackerel broth holds tender fish beneath a warm, tangy onion dressing. Egg, olives, corn, and lettuce complete this traditional La Libertad dish, particularly associated with Holy Week.
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Rinse the salted mackerel, cut it into large pieces, and place it in a bowl with about three fifths of the cold water. Refrigerate for 4 hours, changing the water 3 times. It should retain the character of salted fish without being aggressively salty; desalting is part of the dish, not a step to skip.
Divide the remaining water between two pots. In one, gently simmer the mackerel for 8 to 10 minutes, until the flesh separates easily; remove it, discard the bones, and reserve about 150 ml of strained broth. In the other pot, cook the yellow potatoes, corn, and eggs: remove the eggs after 10 minutes, the corn when tender, and the potatoes when a knife slides in easily.
Peel the yellow potatoes while still warm and pass them through a potato ricer. Add three quarters of the yellow ají paste, half of the vegetable oil, two thirds of the lime juice, part of the salt, and the reserved mackerel broth gradually. Mix until the causa is soft, cohesive, and moldable, moister than a layered Lima-style causa but never runny. Potato and fish should lead, followed by ají and finally lime.
Cut the red onion into thick wedges. Heat the remaining vegetable oil in a skillet and cook the ground garlic, annatto, and remaining yellow ají paste for 1 minute. Add the onion and cook for 2 to 3 minutes, just until the raw edge disappears while it retains some bite. Add the red wine vinegar, oregano, remaining lime juice, and salt; boil for 30 seconds and turn off the heat. The onion dressing should remain tangy, glossy, and firm, not cook down into a soft sauce.
Place lettuce leaves on each plate and shape a thick portion of causa with a slight hollow in the center, recalling the traditional lapa form. Arrange pieces of mackerel in and over the potato and spoon the still-warm onion dressing on top. Finish with quartered egg, black olives, and corn on the side. Serve immediately: the causa should be cool or at room temperature while the onion dressing retains some warmth. 🐟
