Wash the leeks, slice them into half rings, and place them in a different saucepan of boiling water. Boil until softened (usually 8mins). Place in an ovenproof dish.
Melt butter in a saucepan and add the flour, gradually adding milk. Keep stirring to avoid lumps. Simmer for 5mins.
Preheat the grill to high.
Add the mustard and half of the cheese to the butter, flour & milk, simmer for 3 mins, then season with black pepper and salt. Slice the ham into thin strips, add to a saucepan, and simmer for 2 minutes.
Drain the pasta and mix with leeks in an ovenproof dish. Quarter the hard-boiled eggs and place them on top.
Pour the contents of the saucepan on top of the leeks & pasta. Sprinkle the breadcrumbs and the remaining cheese on top. Grill for 10 minutes or until the top turns golden.