Bring a large pot of salted water to a rolling boil. Add the cavatappi and cook until just al dente, about 8 minutes. Drain and reserve ½ cup of the cooking water. Set aside.

If using fresh lobster, steam the tails for 6-7 minutes, then remove the meat from the shells, chop coarsely, and set aside. If using pre-cooked lobster, chop it now.

In a heavy saucepan, melt 3 tbsp unsalted butter over medium heat. Whisk in 3 tbsp all-purpose flour and cook for 1 minute to form a roux.

Slowly whisk in the warmed 2 cups whole milk, cooking until thickened (about 3-4 minutes). Stir in ½ cup heavy cream, then add the shredded cheddar, Gruyère, and Parmesan, stirring until smooth. Season with smoked paprika, black pepper, and sea salt.

In a large mixing bowl, combine the cooked pasta, chopped lobster, and half of the cheese sauce. Toss gently, adding a splash of the reserved pasta water if the mixture seems too thick.

Lightly grease a 9-inch square baking dish and pour the pasta-lobster mixture into it, spreading evenly. Spoon the remaining cheese sauce over the top.

In a small bowl, mix ½ cup panko breadcrumbs with 2 tbsp melted butter until coated. Sprinkle the breadcrumb mixture evenly over the casserole.

Preheat the oven to 375°F (190°C) and bake for 20-25 minutes, until the topping is golden brown and the sauce is bubbling at the edges.

Remove from the oven and let it rest for 5 minutes before serving.