Boil russets in salted water until fork tender, about 15 minutes. Drain and let cool. Pass the russets through a ricer into a big bowl or mash by hand.
In a frying pan, heat olive oil on medium. Remove the sausage meat from the casings and crumble. Fry for about 10 minutes, until crispy. Drain the sausage and put in bowl.
In a large mixing bowl, add potatoes, eggs, Mozzarella and Grano Padano cheese (can be substituted by Parmigianino, cheddar, etc). Throw in crisped sausage, fresh parsley, sea salt and lots of freshly cracked pepper. Mix until almost smooth.
Preheat oven to 350 F.
Grease the baking dish with 1 tbsp of unsalted butter. Lay down half the potato mixture and a layer of smoked Scamorza. Top off with the remaining potato mixture, small pats of unsalted butter (2 tbsp) and sprinkle with breadcrumbs. Bake for 30 minutes, until crust is golden.
Recipe courtesy Food Network Canada