Put a splash of olive oil in a medium saucepan over a low heat, add the leeks and sweat until softened. Pour in the milk and bring to the boil, add the mustard and the blue cheese and simmer for 5 minutes.
Mix the cornflour and 2 tsp water in a bowl then whisk into the milk mix. Stir until thickened and season to taste. Chop the ham into pieces and stir through.
Cook the pasta according to the pack instructions (until firm to the bite) then drain off and run under cold water. Mix in with the sauce.
Pour the pasta into a large ovenproof dish and top with grated cheddar cheese. Grill under a medium grill until golden.
Cook's tip: Find out more about Vintage Farmhouse Cheddar
See more chedder recipes
Haven't got time to cook this from scratch?
Try our ready-made version - Tesco macaroni cheese.