I make this ahead of time every year and freeze it. On Xmas morning, just take it out of the freezer to thaw. Place in 350' oven an hour before serving.

WHIPPED POTATO CASSEROLE
12 to 20 potatoes
Salt and pepper
1/4 cup butter or chicken broth
1/2 pkg cream cheese
1 cup sour cream
Wash and peel potatoes and cook in water until tender. Mash with butter (or chicken broth) and add cream cheese, sour cream, salt and pepper. Mix until smooth and creamy.

Spoon into greased 2 quart casserole dish. Cover with plastic wrap until needed. To reheat, remove from refrigerator, let sit 30 minutes. Preheat oven to 350 deg F. Bake 30 minutes.

I've done them similar to the recipe below but did them the day before not 2 days. However, according to this you can do it 2 days.

I'd rather do it this way than to mash them on the day you're serving.

Here is a link that might be useful: Mashed potatoes

my best suggestion is to make them in the morning and then put in a crockpot on low with a paper towel between the top of the pot and the lid. They keep perfectly fresh for hours.
Jo

Judging from the fact that I have successfully reheated potatoes for several days after they were made, I think you can easily cook them 2 days ahead, even 3 days.

I would cook the potatoes and then mash and add half the milk and butter you normally would. Cool completely before storing them in airtight containers in the fridge, else the condensation will water them down.

On the day you're serving them, transfer them to a pot and bring them to room temp. Thirty minutes before serving, add the rest of the milk and butter and heat on medium low, partially covered. Stir them often to prevent burning.
Sue

We had really cheap potatoes here for about a week last summer. Don't know what got into me, but I ended up with 15 pounds of potatoes. I made up batches of scalloped potatoes (baked and froze them). But back to your question -- I peeled, cut, boiled and seasoned potatoes. Drained and cooled them - then packaged them and froze for future mashed potatoes. Just defrost, heat, mash and add your usual ingredients to finish up. Be sure to cook off the excess moisture after draining (that's something I always do anyway, but particularly important before freezing). I use a Food Saver vacuum sealer for freezing. If you have a vacuum sealer, you could prepare them to the mashing stage and seal and store in your refrigerator for a few days without a problem. I would reheat in a double boiler or in a bowl over hot water.