Seafood Gratin Recipe tastes rich, creamy, and a little bit fancy while still feeling like cozy comfort food, and it works perfectly for weeknight dinners or special occasions in about 50 minutes total. This dish suits seafood lovers who crave a restaurant-style baked seafood casserole with a golden, cheesy breadcrumb topping. I first made a version of this on a tiny apartment stove in Boston, and my neighbors still talk about that buttery aroma that drifted into the hallway.

Why You Should Try This Seafood Gratin Recipe

This Seafood Gratin Recipe gives you tender shrimp, scallops, and flaky fish tucked into a creamy garlic sauce with a cheesy, crisp top. It tastes like something you ordered at a coastal bistro, but you cook it in one baking dish with simple pantry ingredients.

You control the seafood mix, the richness of the sauce, and the amount of cheese, so it fits both special-occasion dinners and casual Sunday meals. Leftovers also reheat surprisingly well, which makes this a smart make-ahead option.

“This Seafood Gratin Recipe tastes like a splurge at a seaside restaurant, but it comes together in one pan at home and disappears in minutes. ★★★★★”

Ingredients You’ll Need

Seafood

Use about 1½ pounds total seafood. Mix and match based on what you like and what your store carries.

8 ounces raw shrimp, peeled and deveined
- Medium or large work well; frozen shrimp thaw quickly in cold water.
6–8 ounces sea scallops or bay scallops
- Pat them very dry so they do not water down the sauce.
6–8 ounces firm white fish, cut into 1-inch chunks
- Cod, haddock, halibut, or pollock all hold up nicely.
Optional: 4–6 ounces lump crab meat
- Use refrigerated pasteurized crab if fresh costs too much; drain it well.

You can use only shrimp, only fish, or a mix of whatever you have. Just keep the total weight close to 1½ pounds so the sauce-to-seafood ratio stays balanced.

Sauce & Flavor Base

3 tablespoons unsalted butter
1 tablespoon olive oil
1 small shallot or ½ small onion, finely minced
3 cloves garlic, minced
3 tablespoons all-purpose flour
1½ cups whole milk or half-and-half
- Whole milk gives a lighter sauce; half-and-half gives a richer one.
¼ cup seafood stock, clam juice, or low-sodium chicken broth
- Pantry shortcut: use chicken broth if you do not keep seafood stock.
½ teaspoon Dijon mustard
½ teaspoon kosher salt, plus more to taste
¼ teaspoon black pepper
¼ teaspoon paprika
Pinch of cayenne or red pepper flakes, optional, for gentle heat
1 tablespoon lemon juice, plus extra wedges for serving
2 tablespoons chopped fresh parsley or chives

Cheese & Topping

¾ cup grated Gruyère or Swiss cheese
- Pre-shredded works in a pinch, but freshly grated melts smoother.
¼ cup grated Parmesan cheese
¾ cup panko breadcrumbs
- Regular breadcrumbs work, but panko gives a lighter crunch.
2 tablespoons melted butter
1 teaspoon garlic powder
½ teaspoon dried thyme or Italian seasoning
Small pinch of salt

Optional Add-ins

½ cup frozen peas, thawed and patted dry
½ cup sautéed sliced mushrooms
½ cup blanched small broccoli florets

These add-ins stretch the dish and sneak in extra veggies without much effort.

Equipment

9×9-inch or similar 2-quart baking dish
Medium saucepan
Medium skillet (if you pre-sear anything)
Whisk
Mixing bowl
Cutting board and sharp knife
Measuring cups and spoons

Tips & Tricks

Pat all seafood very dry with paper towels so the sauce stays thick and creamy.
Cut fish into similar-size pieces so everything cooks at the same pace.
Use room-temperature milk or warm it slightly so the sauce thickens smoothly without lumps.
Whisk the flour into the butter slowly and cook it for at least 1 minute to avoid a raw flour taste.
Add the milk in small splashes while you whisk so the sauce stays silky.
Season the sauce generously; seafood tastes best with enough salt, acid, and a little pepper.
Stir in lemon juice at the end of cooking the sauce so the citrus flavor stays bright.
Mix the seafood into the warm sauce gently so you do not break up the fish.
Keep the baking dish in the upper third of the oven so the topping browns nicely.
If the top browns too fast, tent the dish loosely with foil and move it to a lower rack.
Use pre-shredded cheese and store-bought broth when you want a faster prep.
Let the gratin rest 5 to 10 minutes after baking so the sauce thickens slightly and serves neatly.

How to Make Seafood Gratin Recipe

Step 1: Prep the Oven and Baking Dish

Preheat your oven to 400°F (200°C). Grease your baking dish lightly with butter or a little olive oil. Set it aside while you prepare the sauce and seafood.

Step 2: Prep the Seafood

Peel and devein the shrimp if needed, then pat them dry. Cut the fish into 1-inch chunks and pat dry as well. If you use scallops, dry them thoroughly and cut any very large ones in half so they match the size of the shrimp.

If you use crab meat, pick through it quickly to remove any bits of shell. Keep the seafood chilled in the fridge while you start the sauce. Chilled seafood holds its texture better when it goes into the hot oven.

Step 3: Build the Flavor Base

Place a medium saucepan over medium heat and add the butter and olive oil. When the butter melts and starts to foam slightly, add the minced shallot or onion. Stir and cook until it turns soft and translucent, about 3 to 4 minutes.

Add the garlic and cook 30 seconds until it smells fragrant. Sprinkle the flour over the mixture and stir it in well. Cook this mixture for about 1 to 2 minutes while you stir so it turns slightly golden and smells nutty.

Step 4: Make the Creamy Sauce

Pour in the milk or half-and-half a little at a time while you whisk constantly. The mixture will look thick at first, then smooth out as you add more liquid. Add the seafood stock or broth and keep whisking until the sauce turns smooth and starts to bubble gently.

Stir in the Dijon mustard, salt, pepper, paprika, and cayenne if you use it. Lower the heat slightly and let the sauce simmer for 3 to 5 minutes while you stir often, until it thickens to a gravy-like consistency. Turn off the heat, then stir in the lemon juice and fresh herbs.

Taste the sauce and adjust with a pinch more salt, pepper, or lemon juice if needed. The sauce should taste slightly more seasoned than you think you need, because it will coat plain seafood. Stir in the Gruyère or Swiss cheese and half of the Parmesan until they melt into the sauce.

Step 5: Combine Sauce and Seafood

Place all the prepared seafood in a large mixing bowl. If you use peas, mushrooms, or broccoli, add them now. Pour the warm cheese sauce over the seafood.

Stir gently with a spatula so you coat everything without breaking up the fish pieces. Transfer the mixture into the greased baking dish and spread it into an even layer. The sauce should just cover the seafood; small bits peeking through the top work fine.

Step 6: Mix the Crispy Topping

In a small bowl, combine the panko breadcrumbs, remaining Parmesan, garlic powder, dried thyme or Italian seasoning, and a pinch of salt. Pour in the melted butter. Toss everything together until the crumbs look evenly coated and slightly clumpy.

Sprinkle the breadcrumb mixture evenly over the seafood and sauce. Try to cover the surface fully so you get a nice crust. If you like an extra cheesy top, add a light sprinkle of more Gruyère or Parmesan over the crumbs.

Step 7: Bake the Seafood Gratin

Place the baking dish on the middle or upper rack of the preheated oven. Bake for 18 to 22 minutes, until the topping turns golden brown and the sauce bubbles around the edges. The seafood should turn opaque and just cooked through.

If the top browns too quickly before the seafood cooks, move the dish to a lower rack and cover it loosely with foil. When it finishes baking, remove the dish from the oven and let it rest 5 to 10 minutes. Garnish with extra chopped herbs and a squeeze of fresh lemon before serving.

What to Serve with Seafood Gratin Recipe

Serve this Seafood Gratin Recipe with a simple green salad tossed with a light vinaigrette to balance the richness. Crusty bread or warm garlic bread works perfectly to scoop up the creamy sauce. Steamed green beans, roasted asparagus, or sautéed spinach all pair nicely and keep the plate colorful.

You can also spoon the gratin over plain rice, buttered noodles, or mashed potatoes for a heartier meal. A cold sparkling water with lemon or lime makes a refreshing drink alongside this cozy seafood bake.

Storage Options

Cool leftovers to room temperature, then cover the baking dish tightly or transfer portions to airtight containers and store in the fridge for up to 2 days.
Reheat single portions in the microwave at 50 percent power in short bursts, or reheat larger portions in a 325°F oven until hot in the center.
If you want to freeze, assemble the gratin but skip baking, wrap tightly, and freeze up to 2 months; thaw in the fridge overnight, then bake as directed, adding a few extra minutes if needed.
Avoid repeated reheating cycles so the seafood stays tender and does not turn rubbery.