Cook the pasta – Boil the macaroni in well-salted water until just al dente, then drain thoroughly.

Make the roux – Melt the butter in a saucepan over medium heat, add the flour, and cook gently for 1 minute, stirring constantly.

Add the milk gradually – Pour in the milk a little at a time, whisking continuously until the sauce is smooth and thickened.

Season the sauce – Stir in the mustard, salt, and black pepper to build flavour.

Add the cheese – Remove the pan from the heat and mix in most of the grated cheese until fully melted and smooth.

Combine pasta and sauce – Fold the drained macaroni into the cheese sauce, coating evenly.

Assemble the dish – Spoon the mixture into an ovenproof dish and sprinkle the remaining cheese on top.

Bake until golden – Bake in a preheated oven at 200°C (180°C fan) for 20–25 minutes until bubbling and lightly golden.

Rest briefly – Allow the dish to stand for a few minutes before serving so the sauce settles.