Clearly Pioneer Woman's Mashed Potatoes go well for reheating because of the ridiculous amount of fat in them. If you make your original recipe, make sure to use loads of butter along with the sour cream, and use whole fat sour cream as well. If they are too watery, they will surely dry out in the oven/microwave when reheating or create a starchy coating on the top.

Eh, as a once-a-year treat, they won't kill ya. Definitely one of her more over-the-top dishes, though.

I have read that you can make ahead, but you need to stir from time to time while reheating. I don't like the idea of it, but the mashed are such a pain. I wouldn't put that amount of butter and cream cheese in mashed potatoes as the PW recipe has for my family.

I was just about to recommend PW's mashed potatoes for reheating purposes. My former roommate is a huge mashed potato fan, and she said PW's recipe reheats better than any she's ever had. (although what you've shared sounds delicious, AntoniaJames.. potatoes + roasted onions + sour cream + rich stock = YUM)

Last year, I prepared Pioneer Woman's mashed potatoes (sans Lawry's, though) the day before Thanksgiving, and served 'em up the next day. They are truly over the top delicious and they heat up beautifully. Definitely making them again this year.

http://thepioneerwoman.com/cooking/2007/11/delicious_creamy_mashed_potatoes/

I'm pretty sure you can make 'em. Spread 'em I'm Corningware and then heat 'em up either covered in cheese or foil at 375 for 40 minutes or so and they'll be scrumptious.