How to Make It
Preheat oven to 400°F. Place potatoes, 1 teaspoon of the salt, and water to cover in a Dutch oven. Bring to a boil over medium-high. Reduce heat to medium, and cook until tender, 15 minutes. Drain.
Add sour cream, cream cheese, and butter to potatoes, and mash with a potato masher until almost smooth. Stir in half-and-half, shredded cheese, black pepper, and remaining 1 1/2 teaspoons salt. Lightly coat a 9-inch square pan with cooking spray. Spoon potato mixture into prepared pan. Stir together breadcrumbs, onions, and parsley. Sprinkle mixture evenly over potatoes.
Bake in preheated oven until thoroughly heated, about 20 minutes, covering with aluminum foil after 12 minutes to prevent breadcrumb mixture from overbrowning. Serve immediately.