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1
Soak and Flake the Cod
24 Hours Soaking + 10 Mins
Cold water, ~20°C (68°F)
Soak 500 g of salt cod in cold water for 24 hours, changing the water 3–4 times. Drain, pat dry, pull off the skin, pick out any bones, and flake the flesh into bite-size pieces.
Keep the flakes chunky — they should stay visible in the finished gratin, not dissolve into the sauce.
Done when: Flakes are tender, lightly salted, and free of skin and bones.
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2
Fry the Potatoes Golden
12 Mins
Oil at ~175°C (350°F)
Heat the olive oil in a wide frying pan over medium-high heat. Fry the potato cubes in two batches for 5–6 minutes each, turning once, until pale gold at the edges. Lift out with a slotted spoon and drain on paper. Season lightly — the cod brings most of the salt.
Fry in batches — crowding the pan drops the oil temperature and the potatoes go limp instead of crisp.
Done when: Potatoes are golden at the edges and just tender inside.
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3
Soften Onion, Garlic and Cod
8 Mins
Medium heat, ~160°C (320°F)
In the same pan, soften the sliced onion for 4 minutes until translucent, add the garlic for 30 seconds, then stir in the flaked cod and cook for 2–3 minutes until heated through and fragrant. Tip in the fried potatoes and toss everything together, then spread the mixture into a buttered baking dish.
Do not brown the garlic — it turns bitter in seconds, so add it after the onion has softened.
Done when: Onion is soft and sweet-smelling; cod is hot all the way through.
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4
Make the Cream Sauce
10 Mins
Medium heat, ~160°C (320°F)
Melt the butter in a saucepan, stir in the flour and cook for 1 minute. Pour in the milk a little at a time, stirring constantly, then add the cream and simmer gently for 3–4 minutes until the sauce coats a spoon. Stir in 90 g of the grated Gruyere, the nutmeg and the pepper, and taste — it should need little or no salt.
Keep the heat gentle once the cream is in; a hard boil can make the sauce split.
Done when: Sauce is smooth, thick enough to coat a spoon, and the cheese has melted in.
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5
Assemble and Bake
30 Mins
Oven at 190°C (375°F)
Pour the cream sauce evenly over the cod and potatoes in the baking dish and fold it through gently. Scatter the remaining 30 g of cheese and the breadcrumbs over the top. Bake at 190°C (375°F) for 25–30 minutes until golden, bubbling at the edges, and hot right through — the fish should reach 63°C (145°F) in the centre.
If the top browns too fast, cover loosely with foil for the last 10 minutes.
Done when: Top is deep gold and crisp; the sauce bubbles at the edges.
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6
Rest and Serve
5 Mins
Resting, ~20°C (68°F)
Rest the gratin for 5 minutes so the sauce settles and slices hold together. Scatter over the chopped parsley and serve straight from the dish — about 400 g per person.
A wide spoon serves it best; a knife cuts through the creamy layers.
Done when: Slices hold their shape on the plate; the sauce is creamy, not runny.
auto_awesome Finishing Touches & Plating
Let the gratin rest for five minutes before serving — the sauce thickens as it cools slightly, and the first spoonful holds together instead of sliding apart.
Portugal
50m
