Preheat your oven to 190°C (375°F). Lightly grease a 2-quart (approximately 2 liter) baking dish with butter or cooking spray.

Cook the macaroni according to package directions until al dente (firm to the bite). It's important not to overcook it, as it will continue to cook in the oven. Drain the pasta thoroughly and set aside in a large bowl. A good tip is to slightly undercook it by about 1-2 minutes from the package time.

While the pasta is cooking, prepare the cheese sauce. In a large, heavy-bottomed saucepan or Dutch oven, melt 115g (1/2 cup) of butter over medium heat. Ensure the heat is not too high to prevent burning the butter.

Once the butter is melted and slightly foamy, whisk in the 60g (1/2 cup) of all-purpose flour. Cook, whisking constantly, for about 1 to 2 minutes. This process cooks out the raw flour taste and creates a roux. The mixture should be a pale, sandy color and smell slightly nutty.

Gradually whisk in the 750ml (3 cups) of whole milk, about 250ml (1 cup) at a time, ensuring each addition is fully incorporated before adding more. Continue whisking until the sauce is smooth and free of lumps. This gradual addition helps create a silky smooth béchamel sauce.

Bring the milk mixture to a gentle simmer over medium-low heat, stirring frequently. Cook for about 5 to 8 minutes, or until the sauce has thickened enough to coat the back of a spoon. Do not let it boil rapidly.

Stir in the 250ml (1 cup) of heavy cream. Continue to simmer gently for another 2 minutes, stirring occasionally, until the sauce is rich and slightly more viscous.

Remove the saucepan from the heat. Add the shredded Gruyère cheese (200g / 2 cups), sharp cheddar cheese (200g / 2 cups), and grated Parmesan cheese (50g / 1/2 cup) to the warm sauce. Stir gently until all the cheese is melted and the sauce is smooth and creamy. Avoid returning the sauce to high heat after adding cheese, as it can cause the sauce to break or become grainy.

Season the cheese sauce with salt, freshly ground black pepper, and a pinch of freshly grated nutmeg. Taste and adjust seasonings as needed. The nutmeg adds a subtle warmth that complements the cheese and lobster beautifully.

Add the chopped cooked lobster meat (340g / 12 oz) to the cooked macaroni in the large bowl. Gently fold the lobster into the pasta. Be careful not to break up the chunks of lobster too much.

Pour the warm cheese sauce over the macaroni and lobster mixture. Gently stir everything together until the pasta and lobster are evenly coated with the creamy sauce. Ensure all the pasta is submerged in the sauce.

Transfer the mac and cheese mixture into the prepared baking dish. Spread it out evenly.

Optional: For a crispy topping, in a small bowl, combine the Panko breadcrumbs (50g / 1/2 cup) with 15g (1 tbsp) of melted butter. Sprinkle this mixture evenly over the top of the mac and cheese. This step adds a delightful textural contrast to the creamy interior.

Bake in the preheated oven for 20 to 25 minutes, or until the sauce is bubbling around the edges and the topping (if used) is golden brown and crisp. The internal temperature should reach a safe level, and the casserole should be heated through.

Let the Lobster Mac and Cheese rest for about 5 to 10 minutes before serving. This allows the sauce to set slightly, making it easier to serve and preventing it from being too runny.