Bring a large pot of water to boil, add a good pinch of salt and then potatoes. Boil potatoes with their skins until tender, but still firm, approximately 30 minutes.
Preheat oven to 180°C. Prepare 9 by 11 inch casserole contained by greasing with 5 g of the margarine and then evenly covering the container with the Italian bread crumbs, removing any which do not remain stuck to the margarine.
While still hot, peel the potatoes and then use a potato ricer to mash them.
Add 50 g margarine or butter, diced mozzarella, 60 g parmesan and stir well with a fork. At this point add the 3 egg yolks already beaten with a fork along with freshly grated nutmeg, and another pinch of salt to taste. Once again mix well with the fork.
Transfer the potato mixture into the prepared pan. Then sprinkle the remaining bread crumbs over the top, followed by the remaining parmesan cheese. Then dot the top of the casserole with margarine.
Place casserole in preheated oven for approximately 30 minutes or until golden brown.
This is good just out of the oven or at room temperature. Buon Appetito!