Cook the macaroni according to the packets instructions, drain and set aside.
Whilst the marcaroni is cooking, make the sauce. In a large saucepan, melt the butter over a medium heat. With a large hand whisk add the flour and whisk continuously for a minute. Top tip: I find using a large hand held balloon whisk, you are less likely to have lumps.
Gradually whisk in the milk, a little at a time. Cook for around 10 mins until thickened and smooth.
Remove the sauce from the hob, add the cheese and stir until it is well combined and melted and season.
Pre-heat the grill on a medium heat.
Add the macaroni to combine, tip into a oven proof dish. Sprinkle with extra grated cheese. Place under the grill until the cheese starts to melt and turns golden. Serve immediately.