Hake cooked Basque-style in a pale green sauce of olive oil, garlic and parsley thickened by the fish's own gelatin, garnished with clams, green peas, white asparagus, and wedges of hard-boiled egg. Gentle and clean, it is the Basque coast's signature treatment of its most prized fish — the green sauce (salsa verde) that the region is known for, in its most complete dressed-up form. The hake stays barely set; the sauce is built by swirling the pan, not by adding flour.
Hake (merlu in French, legatza in Basque) is the most esteemed fish of the Basque coast, and merluza en salsa verde is the canonical Basque way to cook it. The koskera garnish — clams, peas, asparagus and egg — is the dressed-up festive version, named in San Sebastián tradition for the koxkeros, the old-town parish folk. The dish is shared across the Basque Country; on the French side around Saint-Jean-de-Luz it belongs to the same green-sauce repertoire, distinct from the plain salsa-verde hake of the Spanish side.
Soft, large flakes of white hake in a sauce that is more emulsion than gravy — glossy, faintly green from the parsley, smelling of garlic and the sea. Clams pop open through it, sweet peas and tender asparagus give bursts of green, and the egg adds a soft, rich note. Nothing is browned or heavy; the whole plate is pale, fresh and built around the delicacy of the fish.
The green sauce is an emulsion: gentle heat and constant swirling of the pan coax gelatin and protein out of the hake — especially from a gelatinous cut near the head — to bind the olive oil and the water the clams release into a glossy, thickened sauce, with no flour at all. The motion matters; rocking the pan keeps the fat and water suspended rather than splitting. The fish is poached only to the point of setting, since hake turns dry and woolly if overcooked, and the clams are added near the end so they open without toughening.
Variations
The plain version is simply merluza/merlu en salsa verde — hake in green sauce with clams alone, no garnish. The full koskera adds peas, asparagus and egg for a feast plate. Cod or other white fish can stand in, and some cooks add a few clams' worth of cider or white wine to the sauce. The same green-sauce technique underlies many Basque seafood dishes.
On the Palate
Where Merlu Koskera sits in the French flavor cloud
Ingredients
Serves 4
How it's made
5 steps · 30 min active + 10 min waiting
- 18 min
Season hake pieces lightly with salt and dust the skinless cut sides with a little flour if you wish.
- 25 min
Warm olive oil with finely chopped garlic in a wide pan until fragrant but not coloured.
- 312 min
Lay in the hake and rock the pan steadily over gentle heat, spooning the oil over, so the fish releases gelatin and the sauce begins to thicken.
Watch outRock the pan steadily over gentle heat, spooning oil over — that constant motion coaxes gelatin from the hake to emulsify the sauce; hold it still and the fat and water split.
- 48 min
Add the clams, peas, cooked asparagus tips and chopped parsley, and continue swirling until the clams open and the sauce is glossy and emulsified.
Watch outAdd the clams near the end and swirl only until they open and the sauce turns glossy — poach the hake just to set, since it goes dry and woolly if overcooked.
- 54 min
Slide in wedges of hard-boiled egg to warm through, adjust seasoning, and serve straight from the pan.
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