Place peeled, cut potatoes in a large pot. Cover with cold water and bring to a rapid boil, reduce heat and simmer until potatoes pieces are tender (just turned tender, do not over cook as the pieces will take on water).
8 large russet potatoes
Preheat your oven to 375°F (190°C).
Drain cooked potatoes into a colander. While potatoes are hot, push them through a fine sieve or use a ricer to mash into a clean pan or large bowl.
Slowly stir in butter (in 1 tablespoon pats) until melted and incorporated, then add warmed cream.
1 cup unsalted butter, ¾ cup heavy cream
Season with salt and pepper, to taste. Stir in mozzarella and Parmesan cheese then transfer into a baking dish.
¼ teaspoon each, salt & pepper, 1 cup mozzarella cheese, ½ cup Parmesan cheese
Parmesan Topping
In a small bowl, melt butter in 30-second increments in the microwave. Add breadcrumbs, Parmesan cheese, and chopped parsley (reserve half of the parsley if you want some for garnish after baking).
4 tablespoon butter, ½ cup bread crumbs, 2 tablespoon Parmesan cheese, 1 tablespoon parsley
Sprinkle topping over your mashed potatoes. Bake at 375°F (190°C) for 20 minutes, or until the topping is golden brown.