Preheat the oven to 400 degrees F. Boil the potatoes until fork tender and let cool. Heat up half the olive oil in a saucepan. Add the diced pancetta and chopped onions. Cook until the onions are golden in color and the pancetta is crisp. In a mixing bowl, mash the potatoes. Add an egg, the cooked onions and pancetta, the grated Parmigiano cheese, Parmigiano chunks and salt, and black pepper, to taste. Mix well until all the ingredients are evenly distributed. Grease a baking dish with the remaining olive oil and add half the bread crumbs to the base of the dish and set aside. Transfer the potato mixture to the baking dish and spread the mixture evenly over the pan, packing the mixture so it serves as a solid bed. Add the remaining breadcrumbs on top. Bake for 20 minutes or until the breadcrumbs are golden brown.
For a creamier texture, use a potato ricer.