Grandma would make these potatoes in this huge bowl a day ahead of the family dinners and let it set in the fridge over night to marinate, then bake it the next day, hence the kids decided they had to rot over night. Now if there was any left over the next day they made potatoe cakes out of the left overs.
Peel and quarter potatoes. Place in boiling water. Cook until tender. Drain, add cream cheese, butter, garlic salt, sour cream, salt, pepper, and mash. Blend together well. Place in casserole dish and cover with plastic wrap. Place in fridge over night. The recipe actually says to leave it there for at least 3 days. I usually cook it the next day. But I might have to test the 3 day to see if it taste different.
On the day you're ready to serve it, place it in the oven(uncovered) at 325 for about 45 minutes, take out add cheddar cheese to the top and bake another 15 minutes. We eat so much of this that 5 potatoes won't do for us I have to use 5 pounds and adjust the amounts. Enjoy.