Preheat the oven to 350°F (180°C).
Cook the potatoes in salted boiling water for 40 minutes. Let them cool, then peel and rice or shred the potatoes into a large bowl.
Add ½ cup (50 g) of grated parmesan, the eggs, salt, pepper and nutmeg. Mix well.
Slice the mortadella and the prosciutto into strips. Cut the mozzarella and the scamorza into pieces.
Add to the potato-egg mix.
Put into a greased baking dish.
Smooth the surface then sprinkle with the rest of the parmesan mixed with the breadcrumbs.
Dot with butter.
Bake for 15 minutes. Increase oven temperature to 400°F (200°C) and bake for another 15 minutes.
Remove from oven and let cool at least 10-15 minutes before serving.