- Prep
- 30 min
- Cook
- 45 min
- Total time
- 75 min
- Yield
- 6 servings
- Difficulty
- Medium
- Calories
- 490 kcal
Quick summary
“Inspired by the traditional British fisherman's pie, this gratin combines cod, salmon, and shrimp in a velvety cheese sauce under golden mashed potatoes. A unique dish that comforts.”
What you need to know
- Velvety seafood sauce: the roux with fish stock, milk, and cheddar creates the viscous base that envelops the fish.
- Cooking fish in the oven: placing cubes of raw fish in the sauce before baking ensures they cook without drying out.
- Golden mashed potatoes with egg yolk: incorporating egg yolk and butter into the puree ensures a rustic crust in the oven.
Ingredients
Main
- tablespoons Olive oil
- unit, medium, finely chopped Cebola
- cloves, minced Garlic
- tablespoons All-purpose flour
- ml Whole milk
- ml Fish stock
- teaspoon Dijon mustard
- g, grated (for the sauce) Cheddar cheese
- g, grated (for gratinéing) Parmesan cheese
- g, skinless and boneless, in 2-3 cm cubes Cod fillet (or hake)
- g, skinless, in 2-3 cm cubes Salmon fillet
- g, cleaned, raw Medium shrimp
- g Fresh (or frozen) peas
- tablespoons, chopped Fresh parsley
- g, asterix or purple type Potatoes (for mashed)
- g (for the puree) Unsalted butter
- ml (for the puree) Fresh cream
- unit (for the puree) Egg yolks
- pinch, freshly grated Nutmeg
- taste Salt
- taste Black pepper
Instructions
Principal
- Prepare the Mashed Potatoes: Cook the potatoes in salted water until very tender. Drain completely, mash them and add the butter, heavy cream, egg yolk, and nutmeg. Season with salt and pepper. The secret to this recipe is getting a smooth and tasty puree, without lumps, which will serve as the perfect topping for the gratin.
- Sauté the Sauce Base: In a large pot, heat the olive oil over medium heat. Add the chopped onion and sauté until translucent, about 5 minutes. Add the garlic and cook for another 1 minute, releasing its aromas. This step is crucial for building a deep and aromatic flavor base for the creamy sauce.
- Make the Roux and Add Liquids: Sprinkle the flour over the onion and garlic, stirring for 1 minute to cook the flour and form a roux. Gradually add the milk and fish stock, whisking constantly with a whisk to avoid lumps. Cook over medium heat, stirring, until the sauce thickens.
- Finish the Creamy Sauce: When the sauce is thick, remove from heat and incorporate the Dijon mustard and grated cheddar cheese, stirring until melted and obtaining a velvety consistency. Season with salt and pepper to taste. The professional technique is to adjust the seasoning at this point, ensuring the sauce is delicious on its own.
- Cook the Fish and Shrimp: Add the cod (or merluza) cubes, salmon, shrimp, and peas to the hot sauce. Gently mix so the ingredients incorporate without breaking the fish. The residual heat of the sauce will help cook the seafood gently, keeping them juicy and tender.
- Assemble the Gratin: Transfer the fish and sauce mixture to a large baking dish (approx. 20x30 cm). Cover evenly with the mashed potatoes. Make grooves with a fork in the mash to create more surface area for crispiness. Sprinkle grated Parmesan cheese on top to brown.
- Bake and Gratinate: Place in a preheated oven at 190°C for 25-30 minutes, or until the filling is bubbly and the mashed potatoes are golden and crispy. In simple terms: the goal is to heat the filling and gratin the topping. Let it rest for a few minutes before serving to set.
Chef's tips
- Drain the water from the potatoes completely before mashing so the puree is firm and can hold the weight of the sauce.
- Cut the fish fillets into medium 3 cm cubes to maintain visual integrity and juiciness after baking.
- Press the back of a fork over the spread mash, forming grooves that caramelize and brown with the parmesan.
Variations
- Leek addition: sauté thin leek slices in butter along with the onion as the base of the creamy white sauce.
- Crunchy crust with panko: sprinkle two tablespoons of panko flour mixed with parmesan over the puree before the oven.
- Individual version in ramekins: assemble portions in individual ceramic baking dishes for refined service.
Substitutions
- Cod fillet: Use hake fillet, yellow croaker, or sea bass cut into boneless cubes.
- Homemade fish stock: use light vegetable broth or additional whole milk added with a pinch of ground bay leaf.
- Grated cheddar cheese: replace with grated aged cheese, mild gouda, or Emmental cheese with great melting properties.
How to store
Keep the gratin in a closed container in the fridge for up to 3 days. Reheat in a preheated oven at 180 °C for about 20 minutes with aluminum foil so the fish heats evenly.
Can it be frozen?
We do not recommend freezing the finished gratin with mashed potatoes. The puree loses its creaminess and acquires a sandy texture upon thawing, while the fish and shrimp release excessive liquid.
What to serve with
Serve accompanied by broccoli or tender green beans sautéed in butter, bitter leaf salad dressed with mild vinaigrette, or slices of rustic bread to enjoy the creamy sauce.
Frequently asked questions
Why put egg yolk in mashed potatoes?
The egg yolk enriches the flavor of the mash and is primarily responsible for giving that golden, shiny color to the top gratinated crust.
Can I use frozen shrimp?
Yes, make sure to thaw beforehand in the refrigerator and drain very well on paper towels so they don't release cold water into the sauce.
Should the seafood be cooked before going into the baking dish?
No, the fish cubes and raw shrimp cook gently inside the simmering sauce in the oven for 30 minutes, remaining juicy and tender.
How to prevent the puree from sinking into the fish sauce?
Let the cheese sauce cool for 10 minutes to firm up a bit in the baking dish and spread the mashed potatoes delicately with a spoon starting from the edges.
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