Preheat the oven to 200 degrees C. Bring a large saucepan of water to the boil. Tip in the macaroni, add a pinch of salt and cook for 3 minutes less than it instructs on the packet. Drain, then return to the pan and keep warm.
Meanwhile, cook the chicken breast in a non-stick frying pan over a low heat for 10 minutes, turning once. Season with salt and pepper, then remove from the pan.
Pour the cream into the frying pan and bring to the boil, scraping the bottom with a wooden spatula to incorporate any browned sediment. Add the milk, nutmeg and salt and pepper to season, if you think it needs it, and heat gently. Cut the chicken into small dice.
Add the diced chicken, cheddar and the creamy milk mixture to the cooked pasta. Mix well.
Pour into a lightly buttered 1.5 litre ovenproof dish or four individual 375ml dishes. Sprinkle with the parmesan and bake a large dish for 30 minutes or individual dishes for 20 minutes, until golden brown.