Choosing sides? Why not have both?

APPARENTLY there are people on the planet who actually think you can serve turkey without potatoes. These are the same traitors who would trot out a cheesecake instead of a pumpkin pie. Traditions are traditions, and potatoes are not just an essential ingredient. You have to have them twice in the same meal.

You need mashed potatoes, creamy and soulful, to soak up the gravy — and sweet potatoes, because they taste both so different and so good with the turkey. Because the sweet potatoes are so often mislabeled as yams, which are a different tuber altogether, it must have been easy for them to slip onto the menu over the nearly century and a half since Thanksgiving became a national holiday.

Because you might eat mashed potatoes at any old meal, they need dressing up for the holiday. But the sweet potatoes, which are less of an everyday thing, actually need to lose a few accessories, starting with the marshmallows and brown sugar.

The best mashed potatoes start at the store. Yukon golds or russets are ideal because of their assertive flavor and excellent texture — buttery in the case of Yukon gold, flaky for russet. But if you find other smooth-textured, full-flavored potatoes at the farmers market, use them. Some taste creamy-rich even before you tear off the wrapper on a stick of Land O’Lakes.

For even cooking, peel them and cut them into chunks (not slices, which turn too mushy). Start them in a big pot of cold water with salt (hot water keeps the potatoes from cooking evenly from the inside out). Cook them at a rolling simmer until they are just soft, not falling apart, then drain them completely and return them to the hot pot.

Now comes the only tricky part. You can mash in as much softened butter as you find conscionable (this is a good day for an artisanal butter, or at least Plugra). Then start mashing in a mixture of cream and milk (it’s a holiday; you need both). The secret here is warming the two liquids so they blend into the potatoes without cooling them down.

No recipe can specify exactly how much liquid you will need for mashed potatoes. The main ingredient varies greatly, not just among varieties but by age, and humidity may even play a part in how much liquid will turn the potatoes creamy but not watery. A good rule of thumb is to add more than you think the potatoes can handle for a light purée, less if you like a dense mound.

Basic mashed potatoes are perfect for sopping up gravy, but the hyper-creamy kind invented by Parisian chef Joël Robuchon have irresistible appeal. His formula involves work that no harried cook with 10 other dishes to get to the table on Thanksgiving Day is going to want to consider, not to mention an obscene amount of butter. A recipe in the newly translated Italian bestseller, “The Silver Spoon,� has a better, quicker idea: Steam rather than boil the potatoes so they aren’t faintly soggy, then replace the milk with mascarpone, the Italian version of cream cheese gone to heaven. This is that sublime situation of a vegetable virtually translated into dairy; it’s like eating solid cream.

The other Thanksgiving potatoes can be just as decadent. Too many cooks spoil the dish with a heavy hand on the sugar when lots of butter and good seasoning will turn them into something truly amazing. Try sweet potatoes just once simply roasted, in the skin, with nothing more than butter and salt, and you will never reach for the brown sugar again.

The best sweet potatoes as turkey partners are the deep orange kind. Long, relatively slender ones are ideal because they are easy to peel and hold their shape when sliced.

And that makes them gratin-ready. Just send them out layered like scalloped potatoes. And instead of sugaring them to compete with cranberry sauce, let them hold their own against turkey and stuffing, not to mention lots of gravy.

Fresh thyme is the perfect herbal partner. It has a grassy liveliness that perks up the underlying flavor. For a jazzier effect, try garlic and chipotle chiles in adobo sauce. The intense sweet taste of the potatoes can stand up to the aggressive seasonings, and the flavor is literally tripled.

And on Thanksgiving, more is better.

Total time: 30 minutes

Servings: 10 to 12

4 pounds Yukon gold or russet potatoes

Sea salt to taste

3/4 cup whole milk

1/2 cup heavy cream

1/2 cup (1 stick) unsalted butter, softened, cut up

Freshly ground white pepper to taste

1. Peel the potatoes and cut into chunks. Place in a large pot and add cold water to cover. Add about 1 teaspoon salt. Cover and bring to a boil over high heat. Uncover, reduce the heat slightly and cook at a steady boil until a test chunk can be easily mashed with a fork, about 10 to 15 minutes.

2. While the potatoes cook, combine the milk and cream in a small saucepan and bring just to a simmer. Set aside in a warm spot.

3. Drain the potatoes well in a colander. Return to the pot and add the butter. Mash until fairly smooth. Gradually mash in the milk-cream mixture. Season with additional salt as needed and white pepper to taste.