Preheat oven to 375°F (190°C). Cook macaroni until al dente, then drain.
In a saucepan, melt butter and whisk in flour. Slowly add milk, stirring until thickened.
Stir in cheddar cheese until smooth. Combine with pasta.
Pour into a baking dish, top with breadcrumbs, and bake 20 minutes until golden.