Place potatoes in a large pot of lightly salted water. Bring to a boil and cook until tender, about 15 minutes; drain.
Transfer potatoes into a large bowl and mash. Stir in sour cream, cream cheese, milk, onion salt, and pepper until well combined. Transfer into a large casserole dish.
Let potatoes cool completely, 15 to 20 minutes. Cover with aluminum foil and refrigerate for up to 2 days.
When ready to bake, remove casserole from the refrigerator and let sit for 30 minutes on the counter. Preheat the oven to 325 degrees F (165 degrees C).
Bake, covered, in the preheated oven for 50 minutes.
Nutritional Facts
Per 12 servings
Calories: 245
Carbohydrate: 36g
Fat: 9g
Fiber: 3g
Protein: 6g
Sugar: 1g
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