HOW TO STORE AND REHEAT MASHED POTATOES
If you have made mashed potatoes in advance, transfer them to a large bowl and cover with plastic wrap or an airtight lid (leaving at least an inch of space between the surface of the potatoes and the wrap/lid). Refrigerate for up to 4 days.  Then you can either reheat the potatoes as follows:
Microwave: Poke a few holes in the plastic wrap and microwave the potatoes on 75% power until hot, stirring every 3-4 minutes.
Crock-Pot: Transfer potatoes to a slow-cooker and heat on “high” for 1 hour, covered, or until hot.
Instant Pot: Transfer potatoes to a pressure cooker and heat on the “warm” setting for 1 hour, covered, or until hot.
Oven: Transfer potatoes to a large stockpot and heat, covered, at 350°F. for 30 minutes, or until hot.
PERFECTLY SMOOTH MASHED POTATOES
5 lb. bag russet potatoes
1 stick butter
½ c. grated Parmesan cheese
½ c. sour cream
½ c. milk
¼ c. cream
Kosher salt and p...