2 oz (60 grams) unsalted butter, plus extra for greasing
1 cup (250 milliliters) fine breadcrumbs
Preheat the oven to 350°F (180°C).
Wash the potatoes. Bring a medium pot with six cups (1.5 l) of water to a boil over medium-high heat. Boil the potatoes for 40 minutes or until they are tender. Remove them from the heat, and let them cool until comfortable to the touch.
Peel the skins off the potatoes, and place the potatoes in a bowl. Discard the skins. Add the milk, and mash the potatoes with a “schiacciapatate” (potato masher).
Transfer the mashed potatoes into a medium bowl. Add the grated Ragusano cheese, whisked eggs, salt, pepper, and nutmeg. Mix well using a wooden spoon. Set aside.
Cut the salami into small cubes, about 1 × 1 inch (2.5 × 2.5 cm). Then, cut the mozzarella cheese into cubes, about 11⁄2 ×11⁄2 inches (4 cm × 4 cm). Add both to the potato purée, and mix well using a wooden spoon.
Grease a 6- x 6-inch (15 x 15 cm) baking dish with unsalted butter, and then cover the bottom of the dish with the breadcrumbs, reserving a little bit for the top. Add the potato purée and spread it evenly across the dish, using a spatula.
Sprinkle the top with the remaining breadcrumbs and little curls of butter.
Place the dish into the preheated oven, uncovered, and bake for one hour or until the top is golden brown.
Remove the dish from the oven, and let it stand for 15 minutes before serving. Serve while still warm. Buon appetito!