Cook the pasta according to pack instructions, drain and set aside.
Melt the butter in a saucepan, add the garlic and cook for a min until softened, then add the mustard powder and cayenne pepper and cook for 1 min more. Add the flour and stir to make a paste, cooking for about 1 min, until the mix starts to bubble a little. Take off the heat and gradually pour in the milk, whisking with every addition so the sauce doesn’t go lumpy. Return to the heat and cook for 5 mins until thickened, then add the cheeses, stir until melted, and fold in the pasta.
Heat oven to 180C/160C fan/gas 4. Tip the pasta into a baking dish, and top with additional cheese, preferably some hard cheese such as cheddar or parmesan, then bake for 25-30 mins, until golden and bubbling. Allow to cool for 10 mins or so then serve.
