Bring a pot of salted water to the boil and cook the macaroni according to the packet instructions. Drain and set aside.
In a frying pan, cook the bacon until crispy. Remove from the pan, chop into small pieces, and set aside.
In the same pan, add the chopped leek to the bacon fat and sauté until soft and fragrant.
Add 1 tablespoon of butter to the pan, stirring until melted. Sprinkle in 2 tablespoons of flour and cook for about 1 minute, stirring constantly.
Gradually pour in 1 ½ cups of whole milk, whisking to prevent lumps. Allow the sauce to thicken. Once thickened, add the Cajun spice, ground nutmeg, and lemon zest. Stir well.
Mix in the grated vintage cheddar until it melts into a smooth, creamy sauce.
Fold in the cooked macaroni, bacon, and crayfish meat. Season with salt and pepper to taste.
Transfer the mixture to an oven-proof dish. Top with breadcrumbs if desired. Bake at 180°C (350°F) for 10-15 minutes, or until golden. Finish under the grill for a few minutes to crisp up the top.
Sprinkle chopped spring onion over the top for a fresh finish. Serve hot, alongside your favourite New Zealand wine or craft beer.
Bring a pot of salted water to the boil and cook the macaroni according to the packet instructions. Drain and set aside.