Bring a large pot of salted water to a boil over medium-high heat. Add the elbow macaroni and cook until al dente, about 8-10 minutes. Once cooked, drain in a colander and set aside.

In a large skillet, melt a tablespoon of butter over medium heat. Add the large shrimp and sauté until pink, about 3-4 minutes. Fold in cooked lobster and crab, cooking for another 2-3 minutes.

In a medium saucepan, melt 4 tablespoons of butter. Whisk in 4 tablespoons of flour to form a roux, cooking for 1-2 minutes. Gradually whisk in 2 cups of milk or cream until the mixture thickens. Incorporate grated cheddar and Gruyère until melted and smooth.

In a large bowl, combine the drained macaroni, seafood mixture, and cheese sauce. Mix well until everything is coated in the sauce.

Preheat your oven to 350°F (175°C). Grease a baking dish with butter, pour in the macaroni mixture, and top with breadcrumbs. Bake for 20-25 minutes until golden and bubbly.