Place potatoes in a large pot and cover with 1 inch cold water. Bring to a boil, reduce the heat, and simmer for 15-20 minutes, until fork-tender. Drain in a colander, then return the potatoes to the hot cooking pot.

Use a potato masher to mash potatoes to your desired consistency.

Stir in sour cream, 1 cup of the shredded cheddar cheese, 1/4 cup scallions, 1 tablespoon parsley, salt, garlic powder, and black pepper. Adjust seasoning to taste.

Transfer to 1-quart baking dish. Sprinkle the remaining 1/2 cup cheese over the top of the potatoes.

Bake for 30 minutes, until heated through. Garnish with remaining 1 tablespoon scallions and 1 tablespoon parsley. Serve hot.