Refrigerator Mashed Potatoes

Here's a recipe I enjoy making for family gatherings. So easy and can be prepared a day ahead.

5 pounds red potatoes (9 large), diced and unpeeled
6 oz package cream cheese
1 cup sour cream
2 teaspoons onion salt
1 teaspoon salt
1/4 teaspoon pepper
4 tablespoons butter

Cook potatoes in boiling salted water until tender. Drain. Mash until smooth. Add remaining ingredients and beat until light and fluffy. Place in oblong baking pan. Cool, cover, and place in refrigerator. May be used anything within two weeks. May reheat in microwave or a 350 degree oven until heated through, about 20-30 minutes.