Cook the pasta in a large saucepan of salted boiling water according to the pack instructions until al dente.
Meanwhile, melt the butter in a large, ovenproof frying pan and stir in the flour to make a smooth paste. Cook until golden, then gradually whisk in the milk. Bring to the boil over a medium heat, then simmer for about 3 minutes until slightly thickened. Remove from the heat, stir in the cheese and season.
Drain the pasta, then tip into the frying pan. Stir into the cheese sauce until well combined. Scatter over the breadcrumbs and Parmesan.
Place in a preheated oven, 190°C (375°F), Gas Mark 5, for 15 minutes or until golden brown and bubbling.