Cook the pasta. Bring a large pot of salted water to a boil. Cook pasta 1 minute shy of al dente. Drain and toss with a small pat of butter to prevent sticking. Set aside.

Prep the lobster. If using cooked lobster, chop it into bite-size pieces. If it’s chilled, gently warm it in a small pan with 1 tablespoon butter and a splash of seafood stock or white wine for 1–2 minutes. Don’t overcook.

Make the breadcrumb topping. Melt 2 tablespoons butter in a small skillet. Stir in panko and toast lightly until pale golden. Remove from heat and mix in Parmesan, parsley, and lemon zest. Season with a pinch of salt and pepper.

Start the sauce. In a large saucepan, melt 4 tablespoons butter over medium heat. If using shallot, sauté it for 1–2 minutes until soft. Sprinkle in flour and whisk to form a smooth paste (roux). Cook 1–2 minutes until it smells nutty but not browned.

Add milk and cream. Slowly pour in the milk and cream, whisking constantly to avoid lumps. Simmer gently for 3–4 minutes until the sauce thickens enough to coat a spoon.

Season the base. Whisk in Dijon, garlic powder, paprika or cayenne (if using), 1 teaspoon salt, and several grinds of black pepper. Taste and adjust.

Melt in the cheese. Reduce heat to low. Add cheddar and Gruyère in handfuls, whisking until smooth after each addition. The sauce should be glossy and pourable, not stiff. If too thick, loosen with a splash of milk.

Combine with pasta and lobster. Fold the pasta into the cheese sauce, coating evenly. Gently fold in the lobster so it stays in nice chunks.

Assemble for baking. Transfer to a buttered 9x13-inch baking dish or similar. Sprinkle the breadcrumb mixture evenly over the top.

Bake. Bake at 350°F (175°C) for 15–20 minutes, until the edges bubble and the top is golden. Let it rest 5–10 minutes before serving so it sets slightly.