After preparing the Make-Ahead Mashed Potatoes, place them in a buttered baking dish or in the crock of your slow cooker if that is how you will be reheating the potatoes. Cover them and store in the refrigerator until ready to reheat. These can be made the day before, which will leave you more time for all your other tasks the day of your dinner. These potatoes are great to serve with a little butter or smothered with your favorite gravy.