For the Stuffed Shells:

Nonstick cooking spray

6 ounces jumbo pasta shells (about 22 shells)

1 tablespoon unsalted butter

1/2 small yellow onion, finely diced

4 cloves garlic, finely chopped or grated

8 ounces shrimp, peeled, deveined, and cut into 1/2-inch pieces

8 ounces bay scallops, cut into 1/2-inch pieces if needed

8 ounces lump crab meat

1/4 cup finely chopped fresh parsley

1/3 cup mayonnaise

1 tablespoon Dijon mustard

1 teaspoon Old Bay seasoning

1/2 lemon, juiced

Kosher salt and ground black pepper, to season

For the Seafood Béchamel Sauce:

3 tablespoons unsalted butter

3 tablespoons all-purpose flour

1 cup clam juice

2 cups half and half

1 teaspoon Old Bay seasoning

Kosher salt and ground black pepper, to season

For the Crispy Breadcrumbs:

1/2 cup panko breadcrumbs

2 tablespoons unsalted butter, melted

Kosher salt and ground black pepper, to season

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Preheat the oven to 350°F (175°C) and lightly coat a 9×13-inch baking dish with nonstick spray.
Cook the jumbo pasta shells in salted boiling water until 2–3 minutes shy of al dente. Drain and set aside.
In a large skillet, melt butter over medium heat. Add onion with a pinch of salt and pepper and cook for 4–5 minutes until softened. Stir in garlic and cook for 1 more minute.
Add scallops and cook for 1 minute, then add shrimp for another 30 seconds. Transfer mixture to a large bowl and combine with crab, parsley, mayonnaise, Dijon mustard, Old Bay, lemon juice, salt, and pepper. Mix well and set aside.
To make the béchamel sauce, melt butter in a skillet over medium heat. Whisk in flour and cook for 1–2 minutes. Gradually whisk in clam juice and half and half, stirring until smooth and thickened, about 3–4 minutes. Season with Old Bay, salt, and pepper.
In a small bowl, mix panko breadcrumbs with melted butter and season lightly with salt and pepper.
Spread 1 cup of béchamel sauce over the bottom of the prepared baking dish. Stuff each shell generously with the seafood filling and arrange in a single layer. Pour the remaining béchamel sauce over the top and sprinkle with the buttered breadcrumbs.
Bake for 30 minutes until bubbly and golden. Broil for an additional 2–3 minutes for extra color, watching closely.
Let rest for 5 minutes before serving. Garnish with extra parsley or chives if desired.

Use lobster, white fish, or langoustines for variation.

Add cayenne or red pepper flakes for a hint of spice.

Stir in Gruyère or Parmesan for a cheesier sauce.

For a lighter version, use milk instead of half and half and skip breadcrumbs.

Assemble up to 1 day ahead and refrigerate before baking.

Store leftovers up to 3 days in the fridge or 3 months in the freezer.