Preheat the oven to 350°F (175°C).
Peel, chop, and boil the potatoes until fork-tender, about 15-20 minutes.
Drain the potatoes and return them to the pot over low heat for a minute to release steam.
Add butter to the potatoes and let it melt before mashing.
Pour in the heavy cream and sour cream, then season with garlic powder, salt, and pepper.
Mash the potatoes until smooth and creamy; avoid over-mashing to prevent gumminess.
Transfer the mixture to a greased baking dish and smooth the top.
Bake for 20-25 minutes until heated through and slightly golden on top.
