Fill a large pot with water and add a pinch of salt. Bring to a boil. Add the cubed potatoes; cook until tender yet still firm, approximately 15 minutes. Drain and transfer them to a large mixing bowl.
Using a potato masher or a fork, mash the potatoes until smooth. Mix in sour cream, cream cheese, butter, onion powder, salt, and pepper. Cover the bowl with plastic wrap and refrigerate for at least 8 hours or overnight.
When ready to bake, preheat your oven to 350°F (175°C). Grease a medium-sized baking dish lightly with oil or butter.
Transfer the potato mixture to the prepared baking dish. Bake in the preheated oven for about 30 minutes until heated through and slightly golden on top.
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