Gather the ingredients.
Cook the potatoes in large pot of boiling salted water until they are tender, about 20 to 30 minutes.
Drain the potatoes in a colander, return the potatoes to the dry pot. Shake over low heat for about 1 minute. This helps make the potatoes fluffy as it drives off excess moisture.
Mash the potatoes until there are no lumps. Beat in the cream cheese, sour cream, onion powder, salt, pepper, and egg.
Place the mashed potatoes in a greased 9 x 13 baking dish. Melt the butter and drizzle over the potatoes. Cool for 20 minutes, then cover and refrigerate up to three days.
Take the potatoes out of the refrigerator about 3 1/2 hours before serving time. Stir the potato mixture well. Remove the potatoes from the dish and place it in a 4- or 5-quart crockpot. Cover and cook on low heat for 3 to 4 hours, stirring once or twice.
You can add more melted butter or some cream or milk if you want a softer consistency. The potatoes can be held in the slow cooker an additional 30 minutes or more on low. Or, turn the crockpot to "keep warm" for another hour or two, if necessary.
Serve and enjoy!