Boil macaroni in salted water until tender; drain.
Melt butter in a saucepan, whisk in flour for 1 minute to make a roux.
Whisk in milk gradually until sauce thickens.
Stir in cheddar cheese, salt, and pepper until melted and smooth.
Mix sauce with pasta, transfer to a baking dish, sprinkle breadcrumbs, and bake at 190°C for 15 minutes.