Halve the leek lengthways, wash and cut into thirds. Cook in salted water for about 10 minutes. Drain the leek and collect the leek broth.
Brush the ham with mustard, spread the leek evenly on top and wrap it. Place in a greased baking dish.
For the sauce, bring the milk and the leek broth with the sauce powder to the boil briefly, season with pepper and nutmeg and pour over the leek rolls. Spread the breadcrumbs evenly over the sauce, dust with paprika and spread the flakes of butter on top.
Bake in a preheated oven at 180 ° C (top / bottom heat) for 25 - 30 minutes. Mashed potatoes also taste very good.