This gratin is rich, savory, and bubbling with a combination of tender seafood, sautéed leeks, and Gruyère cheese. A crisp breadcrumb topping gives way to a creamy interior—flavored with white wine, shallots, Dijon, and herbs. Ideal for chilly nights or when you’re craving something elegant and comforting.
Preheat oven to 375°F (190°C).
Lightly butter or oil a 9-inch baking dish or individual ramekins.
In a skillet, melt 2 tbsp butter over medium heat.
Add leeks, shallot, garlic, and thyme.
Sauté for 5–6 minutes, until soft and fragrant but not browned. Season lightly.
Spread this mixture evenly on the bottom of your baking dish.
In a saucepan, melt 2 tbsp butter. Whisk in flour and cook for 1 minute to form a roux.
Slowly whisk in white wine and let it simmer until reduced by half (about 2–3 minutes).
Gradually whisk in warm milk. Simmer for 5 minutes, stirring until thickened.
Stir in Dijon, nutmeg, salt, and pepper to taste.
Remove from heat and add Gruyère cheese. Stir until melted and smooth.
Toss seafood with lemon juice, salt, and pepper.
Scatter seafood evenly over the leek layer.
Pour cheese sauce over top to just cover the seafood.
In a small bowl, mix breadcrumbs, olive oil, and Parmesan (if using). Sprinkle evenly over gratin
Bake uncovered for 25–30 minutes, or until bubbly and golden on top.
Broil the last 2 minutes if needed for extra browning—but keep an eye on it!
Let cool for 5–10 minutes before serving.
Garnish with chopped parsley and a wedge of lemon if desired.
Serve with warm bread to mop up every last bit of sauce.
Dry the seafood with paper towels before adding to prevent watery sauce.
Don’t overcook—seafood should be just cooked and tender.
You can prepare the leek and sauce ahead and assemble just before baking.
Serve with a white Burgundy, Vermentino, or dry Chenin Blanc. A wine with good acidity balances the richness of the gratin.
4 servings