Preheat the oven to 400 degrees F. Coat baking dish with 1 tablespoon of butter and set aside.

Cook the potatoes in a large pot of salted, boiling water until they are very tender, about 20 minutes. Once cooked, drain out the water and mash potatoes in the same pot. Mash well then mix in the cream, parsley and butter. Add the mozzarella and 1 teaspoon of the parmesan cheese.

Transfer the mashed potatoes to the prepared baking dish. Combine the bread crumbs and remaining parmesan cheese in a small bowl, making sure to blend well. Sprinkle bread crumb mixture over the mashed potatoes. Recipe can be prepared up to this point, 6 hours ahead of time; cover and chill.

Bake, uncovered until the topping is golden brown about 15 minutes.