Classic Fish Gratin with Duchesse Potatoes and Dill Sauce

By Culiora

A classic Swedish fish gratin featuring gently poached cod loins, creamy piped mashed potatoes, and a velvety white wine sauce infused with dill. Baked in the oven until the potato peaks turn a gorgeous golden brown.

• Servings: 4
• Prep time: 25 min
• Cook time: 35 min
• Total time: 60 min

Ingredients

• 600 g cod loin or saithe fillet, cut into portion-sized pieces
• 1/2 pcs lemon, juiced
• 1/2 tsp salt
• 900 g floury potatoes (such as King Edward), peeled and quartered
• 50 g butter
• 1 dl whole milk (3%)
• 2 pcs egg yolks
• 1/2 tsp salt
• 1 pinch freshly grated nutmeg
• 25 g butter
• 2 tbsp all-purpose flour
• 1 dl dry white wine
• 2 dl fish stock (or fish fond diluted with water)
• 1.5 dl heavy cream
• 1/2 pot fresh dill, finely chopped
• 1/4 tsp white pepper, freshly ground
• 1/2 tsp salt

Instructions

1. Preheat the oven to 225°C (conventional heat). Grease an ovenproof baking dish (approx. 20x30 cm).
2. Boil the potatoes in lightly salted water until tender, about 15–20 minutes. Drain thoroughly and let the potatoes steam dry in the pot for 1 minute.
3. Pass the potatoes through a ricer or mash until smooth. Beat in the butter and milk until you have a firm, smooth mash. Finally, stir in the egg yolks and season to taste with salt and grated nutmeg. Let cool slightly so it is easier to pipe.
4. Place the fish pieces in the center of the greased baking dish. Squeeze the lemon juice over the fish and sprinkle with salt. Pipe or spoon the mashed potatoes in an even border around the edges of the dish, creating a well in the center around the fish.
5. Melt the butter for the sauce in a saucepan over medium heat. Whisk in the flour and let it cook, stirring constantly, for 1 minute without letting it brown.
6. Gradually whisk in the white wine and fish stock until completely smooth and lump-free. Add the heavy cream and let the sauce simmer gently over low heat for 4–5 minutes until thickened. Fold in the chopped dill and season to taste with salt and white pepper.
7. Pour the hot sauce over the fish in the center of the dish, taking care not to completely submerge the potato peaks.
8. Bake in the middle of the oven for 18–22 minutes, until the potato peaks are nicely golden brown, the sauce is bubbling, and the fish is just cooked through (internal temperature around 50–52°C). Garnish with a little extra fresh dill before serving.