Peel and cook 5 pounds potatoes in water until tender, drain. Mash until smooth. Mix in separate bowl 6 to 8 ounces cream cheese, 1 cup sour cream, 2 teaspoons onion salt, 1 teaspoon salt, 1/4 teaspoon white pepper, and 2 tablespoons butter. Add to mashed potatoes and mix well. This can be used anytime within 10 days and can be made ahead of time.