Let's start preparing the Potato Gateau by boiling the potatoes in plenty of water with a pinch of salt. They will be cooked in about half an hour, and we can check their cooking by pricking them with a fork. If the potatoes are boiled, they become easy to prick. We immerse them in a bowl of cold water and peel them by pulling away the skin.
Once boiled and peeled, potatoes must be immediately mashed and transferred to a bowl while still hot, so they crumble better, creating a homogeneous, almost creamy mixture.
Cut the mozzarella fiordilatte into slices on a chopping board and let them sit in a colander to lose the excess milk; dice the cooked ham, salami, and provola. The diced meats should be about 1cm thick.
At this point, take the bowl with the potatoes, add softened lard at room temperature, eggs, Pecorino Romano cheese, salami, provola, and cooked ham, also add a sprinkling of pepper, chopped parsley, and adjust the salt. Mix everything until you get a soft and uniform mixture.
Grease the baking dish with extra-virgin olive oil, then coat it with breadcrumbs. Take a part of the Potato Gateau mixture and spread it on the bottom and walls of the baking dish. Fill it with slices of mozzarella fiordilatte, then cover it with the remaining Gattò mixture. Add a layer of breadcrumbs and butter curls on the surface. Prick the top with a fork and bake at 392°F for 40 minutes in a preheated oven. When the top is golden brown, it is ready to be removed from the oven. Serve it warm or cold, cut into slices.