Place the potatoes in a large pot and cover with water. Bring to a boil. Boil for 10-15 minutes, just until you are able to easily pierce with a fork. Take care not to overcook.
Drain potatoes and return them to the pot. Use a potato masher or hand mixer to mash the potatoes. Add the butter and cream cheese to the potatoes. Mash a bit more to incorporate the butter and cream cheese into the potatoes.
Add the sour cream, garlic powder, salt, and pepper to the potatoes and mix until incorporated. Slowly add the heavy cream to the potatoes while mashing or stirring.
Transfer to a serving dish, top with a bit more butter and sprinkle with parsley before serving.
Notes
There's no need to peel the potatoes for this recipe. The skins are so thin, they nearly dissolve into the final potatoes.