Cook the macaroni in a saucepan of fast boiling salted water for 10 minutes and drain well.
Meanwhile, melt the butter in a pan, stir in the flour and cook gently for 1 minute. Remove pan from the heat and gradually stir in the milk. Bring to the boil and continue to cook, stirring, until the sauce thickens, then remove from the heat and add seasonings, 100g cheese and the macaroni.
Pour into an ovenproof dish and sprinkle with the remaining cheese and breadcrumbs.
Place on a baking sheet and bake in the over at 180c for about 20 minutes, until golden and bubbling, or brown under a very hot grill.
