Cook the leeks for about 8 minutes in boiling salted water

Drain

Melt the butter in a pan . Add the flour and cook for a few minutes, gradually whisk in the milk

Add in the mustard and 3/4 of the cheese . Stir well and cook for another 3-5 minutes

Heat the grill

Wrap the leeks in 1 or 2 slices of the ham. Put in a greased dish

Pour over the sauce . Sprinkle over the remaining cheese and breadcrumbs

Place under the hot grill and cook for about 5 minutes until golden

Serve with salad and crusty bread or a jacket potato