Not Crock pot, but I make Make ahead mashed potatoes. Too late for Thanksgiving for this year.
5 pound yellow spuds, I use Yukon Gold
peel and boil in salted water.
Mash with 2 cups of full fat sour cream, 1-2 sticks of butter, grated sharp cheese. Add milk if needed.
I do not measure anymore as I have been making this for 20 years.
Add bacon bits, if your family likes bacon.
Put in a greased casserole dish (I use my lasagne dish), top with more grated cheese and bacon bits.
If you like green onions or chives you can add them too the spuds too.
Cover with plastic and foil. Refrigerate over night, then freeze up to two weeks.
Take out of the freezer the night before. Make sure it is fully thawed and bake in 350 oven until puffed in the middle and the cheese has bubbled and browned a bit.
Tastes like stuffed baked potatoes.
You could probably do it in the crock pot instead of baking in the oven, but the cheese on top will not brown or bubble. I find it cooks up in the time I am resting the turkey and making gravy.