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Monita is a Recipe Tester for Food52
You can make mashed potatoes 1-2 days in advance. To reheat, put the potatoes in heat proof bowl over a pan of simmering water, to re-heat gently. Keep gravy and potatoes separate until serving
Gravy can be made 5 days in advance and kept in the fridge.
June is a trusted source on General Cooking.
You can boil the potatoes a couple of days ahead and refrigerate them, but I wouldn't mash them until just before service. Otherwise they will be just like leftovers! The gravy is another story. You can and should make the stock that is the basis of the gravy as far ahead as you can. However, imho, you'd want to finish it just before serving, after you have the brown bits and drippings from the turkey.
Pegeen is a trusted home cook.
Adding to Monita's point, you can also use a crockpot set on low to keep mashed potatoes warm if you don't have a spare burner, to simmer a bowl of water over. For the gravy, you can make all ahead (even using some some spare turkey parts you roast separately to create extra drippings).
But if you want to add turkey drippings from the day of, just pour them from the roasting pan in the turkey stock you already prepared in advance. Thicken up with a roux if you think it needs it. Let fat rise as it cools, skim off, reheat.
i think June and I were saying the same thing about gravy - most can be done ahead except some last minute drippings and brown bits from roasted turkey.
I'd check out the nyt essential thanksgiving guide, a great resource with answers for the potato and gravy question!
Let the sheet pan do the heavy lifting.
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