Carluccia and her sister, Domenica, prepared this surprisingly easy and unique dish together for dinner one night. Think of this as being akin to a potato lasagna; it is rich and substantial, acting as an easy and affordable main course for many. Be sure to whip the egg whites before incorporating them, and, if possible, use a potato ricer to sieve the potatoes; these two techniques contribute an important airiness to the richness of the pie.
5 pounds mashing potatoes (I use Yukon gold)
1 1/2 tablespoons salt, divided
1 cup milk, warmed
1 1/2 sticks (3/4 cup) butter, at room temperature
3 eggs, separated
1/2 pound smoked mozzarella or provola, cut into small pieces
1/3 pound thinly sliced prosciutto
3 ounces freshly grated Parmesan
3 whole eggs
1/2 cup bread crumbs
Preheat the oven to 375 degrees F, and butter a 9-by-13-inch rectangular baking dish.
Peel the potatoes, and cut them into quarters. Boil them in a pot of water with 1 tablespoon of the salt until soft (about 15 minutes). Press through a potato ricer, or mash well with a hand masher. Gently stir the warm milk, 1 stick of the butter cut into pieces, and the remaining salt into the warm potatoes. Whip the egg whites until they form soft peaks, and fold them in.
Place a layer of mashed potatoes about 1 inch high in the buttered dish. Dot the top with smoked cheese, then a single layer of prosciutto, and finally a generous sprinkling of Parmesan. Create another layer of potatoes, and top it with the cheeses and prosciutto (you should finish the smoked cheese and prosciutto on this layer, but make sure to reserve enough Parmesan for the final topping). Add a final layer of mashed potatoes, and dot with slivers of butter from the remaining 1/2 stick.
Whisk together the egg yolks with the 3 whole eggs. Pour this over the top of the potatoes. Sprinkle with the remaining Parmesan, and then the bread crumbs. Bake for about 40 minutes, or until the top of the potato pie has puffed up and turned a deep golden brown.