Equipment
Ingredients
Seafood Mix
- 300 g cod fillet, skinless, pin-boned, cut into 3cm chunks
- 200 g salmon fillet, skinless, pin-boned, cut into 3cm chunks
- 150 g raw king prawns, peeled and deveined
Leek Base
- 2 leeks, white and light green parts only, sliced into half-moons, washed thoroughly
- 30 g unsalted butter
- 60 ml dry white wine
Cream Sauce
- 40 g unsalted butter
- 40 g all-purpose flour
- 400 ml whole milk, warmed slightly
- 100 ml double cream
- 10 g dijon mustard
- 1 g ground nutmeg
Gratin Topping
- 50 g panko breadcrumbs
- 80 g gruyere cheese, freshly grated
- 20 g unsalted butter, melted
- 10 g fresh flat-leaf parsley, finely chopped
Caramelised Apples
- 3 apples, peeled, cored, and sliced into wedges
- 30 g unsalted butter
- 15 g light brown sugar
- 2 g fresh thyme, leaves picked
Nutrition (per serving)
Method
Preheat your oven to 200C/400F. Generously butter a 1.5-litre gratin dish or 9x9 inch baking dish. Ensure all fish and prawns are patted completely dry with paper towels to prevent a watery sauce.
Melt 30g of butter in a large frying pan over medium heat. Add the sliced leeks with a pinch of salt and sweat them until entirely soft but not browned. This will take about 8-10 minutes.
Increase the heat to medium-high and pour in the white wine to deglaze the pan. Let it bubble rapidly until the liquid has almost entirely evaporated. Remove the pan from the heat and set aside.
In a medium saucepan, melt 40g of butter over medium heat. Whisk in the flour and cook for 1-2 minutes until it smells lightly toasted. Gradually whisk in the warm milk, ensuring no lumps form. Bring to a gentle simmer, whisking constantly until the sauce visibly thickens.
Remove the thickened sauce from the heat. Stir in the double cream, dijon mustard, nutmeg, and a generous seasoning of salt and black pepper. Fold the cooked leeks into this sauce.
In a large bowl, gently toss the raw chunks of cod, salmon, and prawns with the warm leek and cream sauce until evenly coated. Transfer this mixture into the prepared gratin dish, spreading it into an even layer.
In a small bowl, combine the panko breadcrumbs, grated gruyere cheese, melted butter, and chopped parsley. Sprinkle this topping evenly over the seafood mixture.
Bake the gratin in the preheated oven for 20-25 minutes. The sauce should be bubbling fiercely at the edges, the crust deeply golden, and the internal temperature of the fish must reach 63C/145F.
While the gratin is in its final 10 minutes of baking, prepare the apples. Melt 30g of butter in a frying pan over medium-high heat. Add the apple wedges and brown sugar. Cook until the apples are golden brown, lightly caramelised, and tender but still holding their shape. Stir in the fresh thyme right at the end.
Remove the gratin from the oven and let it rest for 5 minutes. This allows the creamy sauce to settle and prevents it from being dangerously hot. Serve the gratin in warmed shallow bowls with the caramelised apples alongside.
Chef's Notes
- Using raw seafood folded into warm sauce ensures perfectly cooked fish. If you pre-cook the fish, it will severely overcook and turn rubbery during the 20-minute bake.
- For an extra layer of flavour, swap the milk in the sauce recipe for a high-quality fish stock, reducing the double cream slightly if you prefer a lighter result.
- The caramelised apples act as an acidic, sweet foil to the ultra-rich dairy and seafood. Do not skip the thyme; the herbal note bridges the gap between the fruit and the savoury main.
- If your leeks are particularly dirty, slice them first, then soak the slices in a large bowl of cold water. Lift them out with your hands so the grit stays at the bottom of the bowl.
Storage
Refrigerator: 2 days — Store in an airtight container. The breadcrumb crust will soften significantly.
Freezer: 1 month — Freeze before baking for best results, though the cream sauce may split slightly upon thawing.
Reheating: Cover with foil and reheat in a 180C/350F oven until bubbling. Remove foil for the last 5 minutes to recrisp the top.
