Prepare the Seafood: Heat a medium skillet over medium heat and melt 2 tablespoons of butter. Add minced garlic and sauté until fragrant. Incorporate lobster and crab meat, cooking for 2-3 minutes, then remove from heat to cool slightly.

Make the Filling: In a large mixing bowl, combine sautéed seafood with cream cheese and shredded mozzarella. Stir until smooth and season with salt and pepper.

Cook the Pasta Shells: Boil a large pot of salted water, add pasta shells, and cook until al dente. Drain and rinse under cold water. Set aside to cool.

Prepare the Sauce: In the same skillet, melt 2 tablespoons of butter. Whisk in flour and cook for 1 minute. Gradually add heavy cream while whisking, then stir in grated Parmesan cheese until smooth.

Assemble the Dish: Preheat oven to 375°F. Pour a thin layer of cheese sauce into a baking dish. Stuff each shell with seafood filling and place in dish. Pour remaining sauce over shells.

Bake: Cover with aluminum foil and bake for 20 minutes. Remove foil and bake for an additional 10 minutes until golden and bubbly.

Serve: Let cool for a few minutes before serving. Optionally, sprinkle with additional cheese or fresh herbs.