Prepare the Noodles: Cook the lasagna noodles according to the package instructions. Drain and set aside.
Cook the Seafood: In a skillet, melt butter over medium heat. Add garlic and sauté until fragrant. Add shrimp and scallops, cooking until just opaque. Set aside and fold in the crab meat.
Make the Sauce: In the same skillet, add flour and cook for 1-2 minutes. Gradually whisk in heavy cream and stock. Simmer until thickened, then season with salt and pepper.
Prepare the Cheese Mixture: In a bowl, combine ricotta, Parmesan, and half of the mozzarella. Mix well.
Assemble the Lasagna: Spread a layer of sauce in the baking dish. Add a layer of noodles, followed by the cheese mixture, seafood, and sauce. Repeat until all ingredients are used, finishing with a layer of mozzarella on top.
Bake: Preheat the oven to 375°F (190°C). Cover the dish with foil and bake for 25 minutes. Remove the foil and bake for an additional 15 minutes until golden and bubbly.
Garnish and Serve: Let the lasagna rest for 10 minutes before serving. Garnish with fresh parsley.