Creamy Dill Fish Gratin with Duchess Potatoes

Why You’ll Love This Recipe

• Classic Swedish comfort: tender white fish in a silky dill sauce under golden duchess-potato swirls.
• Make-ahead friendly for stress-free entertaining.
• Balanced flavors—bright lemon and fresh dill lift the rich, creamy sauce.
• Looks restaurant-fancy but uses simple, affordable ingredients.

Grocery List

• Produce: Potatoes, shallot, fresh dill, lemon, peas or salad greens.
• Dairy: Butter, whole milk, heavy cream, eggs.
• Pantry: All-purpose flour, Dijon mustard, fish or seafood stock, dry white wine (optional), salt, white pepper, nutmeg.
• Seafood: Cod or haddock fillets, cooked shrimp.

Full Ingredients

Fish & Assembly

• 800 g flaky white fish (cod, haddock, or pollock), skinless, pin bones removed
• 1 tsp fine sea salt
• 1/2 tsp ground white pepper
• 1 tsp finely grated lemon zest
• 15 g unsalted butter (for greasing the baking dish)

Dill Cream Sauce

• 30 g unsalted butter (2 tbsp)
• 1 small shallot, very finely minced (about 30 g)
• 30 g all-purpose flour (about 1/4 cup)
• 80 ml dry white wine (optional; substitute same amount of stock if preferred)
• 250 ml fish or seafood stock (about 1 cup)
• 200 ml whole milk (about 3/4 cup + 1 tbsp)
• 100 ml heavy cream (about 1/3 cup + 1 tbsp)
• 1 tbsp Dijon mustard
• 1 tbsp fresh lemon juice
• 2 tbsp finely chopped fresh dill, plus more for garnish
• 1/2 tsp fine sea salt, or to taste
• Pinch ground white pepper

Duchess-Potato Topping

• 900 g floury potatoes (Yukon Gold or russet), peeled and cut into chunks
• 60 g unsalted butter (4 tbsp), softened
• 60 ml heavy cream or whole milk (1/4 cup), warmed
• 2 large egg yolks, room temperature
• 1/4 tsp fine sea salt (plus salt for the potato water)
• Pinch ground white pepper
• Pinch freshly grated nutmeg (optional)

Garnish & Serving

• 150 g cooked cold-water shrimp, peeled
• Steamed peas (150–200 g) or a crisp green salad
• Lemon wedges
• Extra dill sprigs

Step-by-Step Instructions

Step 1: Boil and dry the potatoes

Place the peeled, chunked potatoes in a pot of generously salted cold water. Bring to a gentle boil and cook until tender when pierced with a knife, 15–20 minutes. Drain thoroughly, then return the potatoes to the hot pot and set over very low heat for 2–3 minutes, shaking occasionally to steam off excess moisture.

Step 2: Make the duchess-potato mixture and load the piping bag

Mash or rice the potatoes until smooth. Beat in 60 g softened butter and 60 ml warm cream. Season with 1/4 tsp salt, a pinch of white pepper, and a tiny pinch of nutmeg. When the mash is warm (not hot), quickly stir in the 2 egg yolks until glossy. Transfer to a piping bag fitted with a large star tip; keep at room temperature while you prepare the fish and sauce.

Step 3: Heat the oven and prep the fish

Preheat the oven to 210°C (410°F), conventional heat. Butter a 2-quart (about 2 L) baking dish. Pat the fish dry. Season with 1 tsp salt, 1/2 tsp white pepper, and sprinkle with 1 tsp lemon zest. Lay the fillets in the dish in a single layer.

Step 4: Cook the dill cream sauce

In a saucepan over medium heat, melt 30 g butter. Add the minced shallot and cook until translucent, 2 minutes. Stir in the flour and cook, stirring, 1 minute to make a pale roux. Whisk in the wine (if using), then gradually whisk in the fish stock and milk. Bring to a gentle simmer and cook 3–4 minutes until thickened and smooth. Stir in the cream, Dijon, lemon juice, and dill. Season to taste with salt and white pepper—the sauce should be well seasoned and slightly tangy. Keep hot but not boiling.

Step 5: Assemble the gratin with duchess swirls

Pour the hot dill sauce around and over the seasoned fish in the baking dish. Pipe generous duchess-potato swirls around the rim and a few rosettes or lines across the top, leaving some sauce visible in the center for a classic fiskgratäng look.

Step 6: Bake until tender and golden

Bake on the center rack for 18–22 minutes, until the fish flakes easily and reaches an internal temperature of 52–55°C (125–131°F). If you’d like deeper color on the potato, switch to the broiler for 1–2 minutes, watching closely.

Step 7: Finish with shrimp and dill

While the gratin rests 5 minutes, quickly warm the shrimp by tossing them with a spoonful of the hot sauce (or keep them chilled for contrast). Scatter the shrimp and a few dill sprigs over the top.

Step 8: Serve

Spoon the fish and sauce onto warm plates, adding a few duchess swirls to each. Serve with buttered peas or a crisp green salad and lemon wedges for squeezing.

Pro Tips

• For ultra-smooth potatoes, use a ricer and add egg yolks only after the mash has cooled slightly so they don’t scramble.
• The sauce should be thicker than soup but still pourable; it will loosen a bit in the oven as the fish releases juices.
• Cod and haddock vary in thickness; start checking doneness at 16 minutes for thin fillets.
• Pipe potatoes just before baking so the ridges stay defined and crisp.
• Keep shrimp off the heat until the end to preserve their sweet, tender bite.

Variations

• Cheesy duchess: Fold 40–60 g grated Västerbotten or Parmesan into the hot mash before adding yolks.
• Gluten-free: Swap the flour for 2 tbsp cornstarch. Whisk into cold milk, then add to the hot stock and simmer until thick.
• Veg boost: Nestle blanched asparagus tips or sautéed leeks around the fish before adding the sauce.

Storage & Make-Ahead

Assemble through Step 5 up to 24 hours ahead; cover and refrigerate. Bake from cold at 200°C (390°F) for 25–30 minutes, then broil if needed. Add shrimp after baking. Leftovers keep 2 days refrigerated; reheat covered at 175°C (350°F) for 15–20 minutes, then uncover to re-crisp potatoes. Freezing is not recommended (the sauce can separate and the potatoes may become grainy).

Nutrition (per serving)

Approximate: 680 kcal; 44 g protein; 38 g fat; 49 g carbohydrates; 2.4 g fiber; 1.6 g sodium. Values will vary with fish type, added salt, and side dishes.