Cook the potatoes. Add the cubed potatoes to a large pot, fill with enough water to cover them, and add ½ tablespoon of salt. Set the potatoes over high heat and bring the water to a boil; lower the heat to a steady simmer and cover the pot. Cook for 18 to 20 minutes, or until the potatoes are soft and tender. Remove from heat and drain in a colander.
Combine the ingredients. Put the potatoes back in the pot and add 4 ounces cream cheese, sour cream, and butter. Using a potato masher, mash the potatoes until creamy. For creamier mashed potatoes, add the remaining cream cheese.
Season the mashed potatoes. Stir in the garlic powder, salt, and pepper; taste and adjust accordingly.
Serve. Spoon the mashed potatoes into a serving bowl and garnish with parsley and a pat of butter before serving.