Seafood au Gratin

Essentially a seafood casserole, this seafood au gratin is a cheesy, tender fish dish that gives the impression of a complicated meal but is quite simple to throw together. It does have a fair number of ingredients, but once everything is combined in the casserole dish, you’ll leave it to bake and tenderize until it’s ready. And when it is ready, be prepared for a truly decadent dish: The inside is filled with sauteed mushrooms, tender flaky fish and buttery scallops, and it’s finished with a golden, bubbly cheesy topping. Serve this one with buttery garlic bread and a leafy green salad on the side.

Ingredients for Seafood au Gratin

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• Haddock or cod: You can use a pound of haddock or cod fillets (or a mix of both—they pair well together in a casserole).
• Sea scallops: You can also use bay scallops, if necessary.
• Butter: We recommend using unsalted butter when baking or cooking so you can control the salt content in your dish.
• All-purpose flour: This recipe calls for just 2 tablespoons. Feel free to swap it 1-to-1 for a gluten-free flour mix if you like.
• Pepper: Freshly ground pepper will elevate the pepper flavor.
• Chicken broth: Premade chicken broth works well, or you can make your own chicken broth ahead of time and keep it on hand. (Tip: It freezes well!)
• 2% milk: Whole milk or half-and-half would also work, but be sure it’s at least 2% for the best flavor and creamy texture.
• Cheese: You’ll be using a mix of Parmesan cheese, part-skim mozzarella and shredded cheddar cheese.
• Mushrooms: Sliced fresh cremini mushrooms are particularly easy to work with for this dish.
• Chives (optional): Minced fresh chives are an excellent addition at the end.

Directions

Step 1: Arrange the fish

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Preheat the oven to 350°F. Arrange the fish and scallops in a greased 11×7-inch baking dish, then set it aside.

Step 2: Make the sauce

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In a small saucepan, melt 2 tablespoons of the butter. Stir in the flour and pepper until smooth. Gradually add the broth and milk, and stir until they’re fully combined and creamy. Bring the pan to a boil, then cook and stir for an additional two minutes, or until thickened. Stir in 1/4 cup of each cheese. Set it aside.

Step 3: Prep the mushrooms

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In a small skillet, saute the mushrooms in the remaining 2 tablespoons of butter until they’re tender, then stir the mushrooms into the cheese sauce. Spoon this mixture over the seafood.

Step 4: Top with cheese and bake

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Sprinkle the dish with the remaining mozzarella, cheddar and Parmesan cheese. Cover and bake for 15 to 20 minutes, or until bubbly, golden and the fish flakes easily with a fork. If desired, top it with freshly chopped chives to serve.

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Seafood au Gratin Variations

• Add more veggies: Either keep the mushrooms out altogether, or add in a handful of peas, zucchini or summer squash, or slices of onion. Asparagus is another lovely addition as well.
• Make it with herbs: While making the melted cheese sauce, stir in dried chopped parsley, basil or even thyme or rosemary.

How to Store Seafood au Gratin

Store any cooled leftovers in the casserole dish you baked it in, but keep the top covered well with plastic wrap or foil, then refrigerate.

How do you reheat seafood au gratin?

Keep the casserole dish covered in foil and place it in a preheated oven on low. Allow the casserole to begin to bubble, about 15 to 20 minutes.

Seafood au Gratin Tips

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How do I select quality seafood?

When it comes to cod, look for a white or cream line. In haddock, you want a dark grey or black line. Both cod and haddock should be clean, with a firm white flesh—it should appear translucent, not opaque, as anything that’s opaque is a sign that the meat is not as fresh.

When it comes to selecting scallops, avoid those that are grayed or yellowed, instead selecting those that are creamy white, orange or light pink. Again, scallops should have a slightly translucent appearance as well. Additionally, the scallops should feel firm, not mushy or slimy.

Can I use other fish?

Yes. If cod or haddock aren’t available, you can use other white fish such as walleye, perch, halibut or even flounder in this seafood au gratin recipe.

What should I serve this with?

This creamy, cheesy seafood casserole is a filling meal, so we recommend pairing it with a light side dish. Think steamed vegetables or a favorite asparagus dish.