Place macaroni in a large microwave safe container (at least 3L capacity). Add salt and 1.2L of boiling water, do not cover container.
Place container onto the base of the oven. Select Auto Cook Menu 10 (Dried Pasta), weight 250g and start. Stir pasta when the oven beeps during cooking. Allow pasta to stand for 5 minutes after cooking, then drain.
Whilst the pasta is cooking, prepare the topping by combing all ingredients in a medium sized bowl and set aside.
Whilst the pasta is resting, make the cheese sauce. Over a medium heat, melt the butter in a medium sized saucepan. Add the mascarpone, cheddar, dijon and 3 tablespoons of the pasta cooking water. Season well with salt and pepper and stir until smooth. Add the drained pasta to the sauce and stir well to combine.
Pour macaroni into an oven proof dish. Sprinkle with breadcrumb topping.
Place the wire rack in the oven, and the macaroni dish on top of the rack. Select Auto Cook Menu 20 (Fresh Crispy Top), 500g and start. Keep an eye on it, you may need to remove the macaroni with 2-3 minutes to avoid over cooking. Serve immediately.