- Cook the macaroni in a large saucepan of boiling salted water for 8-10 minutes; drain well and set aside.
- Melt the butter over a medium heat in a saucepan slightly larger than that used for the macaroni. Add the flour and stir to form a roux, cooking for a few minutes.
- Gradually whisk in the milk, a little at a time. Cook for 10-15 minutes to a thickened and smooth sauce.
- Meanwhile, preheat the grill to hot.
- Remove the sauce from the stove, add 175g of the cheese and stir until the cheese is well combined and melted.
- Add the macaroni to the sauce and mix well. Transfer to a deep suitably-sized ovenproof dish.
- Sprinkle over the remaining cheddar and the parmesan and place the dish under the hot grill. Cook until the cheese is browned and bubbling. Serve hot with a side salad or fresh vegetables.