Preheat your oven to 375°F (190°C) and grease a 9x13-inch baking dish.

Cook the lasagna noodles in salted boiling water until they are al dente. Drain them and lay them out on parchment paper to avoid sticking.

In a skillet, melt the butter over medium heat. Add the minced garlic and chopped onion, cooking until they are soft and fragrant.

Stir in the flour to create a roux, cooking for 1 to 2 minutes.

Gradually whisk in the heavy cream and whole milk until the mixture is smooth and has thickened.

Mix in half of the shredded mozzarella and half of the Parmesan cheese. Season the mixture with Old Bay seasoning, paprika, salt, and black pepper, then remove from heat.

In a small bowl, combine the ricotta cheese, egg, and a tablespoon of chopped parsley.

To assemble the lasagna, spread a thin layer of the sauce on the bottom of the prepared baking dish.

Place 3 lasagna noodles on top, then spread with the ricotta mixture, followed by a portion of the shrimp and crab, more sauce, and a sprinkle of mozzarella cheese.

Repeat the layers until all ingredients are used, finishing with a layer of noodles, sauce, and the remaining cheese on top.

Cover the dish with foil and bake for 25 minutes. Then, remove the foil and bake for an additional 15 minutes, or until the top is golden and bubbly.

Allow the lasagna to rest for 10 minutes before slicing. Garnish with the remaining parsley before serving.