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.
Yields 4 Servings Servings Quarter (1 Serving) Half (2 Servings) Default (4 Servings) Double (8 Servings) Triple (12 Servings) Prep Time 20 minsCook Time 35 minsTotal Time 55 minsSeafood
8 oz white fish (cod, halibut, or haddock), cut into chunks
6 oz raw shrimp, peeled and deveined
8 oz bay scallops or chopped sea scallops
Salt and pepper, to taste
1 tbsp lemon juice
For the Leek Base
2 tbsp butter
1 large leek, white and light green part only, thinly sliced and rinsed
1 shallot, finely chopped
1 clove garlic, minced
½ tsp fresh thyme (or ¼ tsp dried)
For the Mornay Sauce (Cheese Béchamel)
2 tbsp butter
2 tbsp flour
½ cup dry white wine
1 ¼ cups whole milk (warm)
1 tbsp Dijon mustard
1 cup grated Gruyère cheese
Salt, pepper, and a pinch of nutmeg
Topping
½ cup panko breadcrumbs
1 tbsp olive oil or melted butter
2 tbsp grated Parmesan (optional, for extra golden crust)
Fresh parsley, chopped (for garnish)
Suggested Sides
Crusty bread or baguette slices
Garlic green beans or roasted asparagus
Simple butter lettuce salad with lemon vinaigrette
Preheat Oven
1
Preheat oven to 375°F (190°C) .
Lightly butter or oil a 9-inch baking dish or individual ramekins.
Prepare the Leeks
2
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.
Make the Mornay Sauce
3
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.
Assemble the Gratin
4
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
5
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!
Serve
6
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.
Tips for Success
7
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.
Wine Pairing
8 Serve with a white Burgundy , Vermentino , or dry Chenin Blanc . A wine with good acidity balances the richness of the gratin.
Ingredients Seafood
8 oz white fish (cod, halibut, or haddock), cut into chunks
6 oz raw shrimp, peeled and deveined
8 oz bay scallops or chopped sea scallops
Salt and pepper, to taste
1 tbsp lemon juice
For the Leek Base
2 tbsp butter
1 large leek, white and light green part only, thinly sliced and rinsed
1 shallot, finely chopped
1 clove garlic, minced
½ tsp fresh thyme (or ¼ tsp dried)
For the Mornay Sauce (Cheese Béchamel)
2 tbsp butter
2 tbsp flour
½ cup dry white wine
1 ¼ cups whole milk (warm)
1 tbsp Dijon mustard
1 cup grated Gruyère cheese
Salt, pepper, and a pinch of nutmeg
Topping
½ cup panko breadcrumbs
1 tbsp olive oil or melted butter
2 tbsp grated Parmesan (optional, for extra golden crust)
Fresh parsley, chopped (for garnish)
Suggested Sides
Crusty bread or baguette slices
Garlic green beans or roasted asparagus
Simple butter lettuce salad with lemon vinaigrette
Directions Preheat Oven
1
Preheat oven to 375°F (190°C) .
Lightly butter or oil a 9-inch baking dish or individual ramekins.
Prepare the Leeks
2
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.
Make the Mornay Sauce
3
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.
Assemble the Gratin
4
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
5
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!
Serve
6
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.
Tips for Success
7
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.
Wine Pairing
8 Serve with a white Burgundy , Vermentino , or dry Chenin Blanc . A wine with good acidity balances the richness of the gratin.
Seafood Gratin with Leeks & Gruyère
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