Place the peeled and cut potatoes in a large pot and cover with cold water by 1 inch. Add a pinch of salt to the water, then bring to a boil over high heat.

Reduce heat to a simmer and cook the potatoes until fork-tender, about 12–15 minutes depending on the size of the pieces. Test by piercing a chunk with a fork; it should slide off easily.

While the potatoes cook, heat the milk and butter together in a small saucepan over low heat until the butter melts and the mixture is warm. Keep warm — don’t boil.

Drain the potatoes well, reserving about 1 cup of the cooking liquid. Return the potatoes to the hot pot and let them sit for a minute to allow excess moisture to evaporate. This helps keep the mash fluffy.

Mash the potatoes using a ricer, potato masher, or sturdy fork. For the fluffiest texture, a potato ricer or food mill works best. Avoid an electric mixer which can make potatoes gluey.

Slowly add the warm milk-and-butter mixture to the potatoes, folding gently until incorporated. If you want extra tang, fold in the sour cream or Greek yogurt at this stage.

If the mashed potatoes feel too stiff, add a splash of the reserved cooking liquid or extra warm milk until you reach your desired consistency. Taste and season with additional salt and pepper.

To make ahead (refrigerator): Transfer the mashed potatoes to an airtight container or a baking dish, smoothing the top. Dot with a few small pieces of butter to help prevent a skin from forming. Cover and refrigerate for up to 3 days.

To reheat from chilled: Preheat oven to 350°F (175°C). Place the mashed potatoes in a buttered baking dish, add a few tablespoons of milk or cream and a couple of slices of butter on top. Cover tightly with foil and bake for 20–30 minutes, stirring halfway through, until heated through and fluffy. Alternatively, reheat gently on the stovetop over low heat, stirring frequently, and adding milk as needed.

To reheat from frozen: Thaw overnight in the fridge, then reheat by the oven method above. If reheating straight from frozen, allow extra time and check center temperature before serving.

Just before serving, fluff the potatoes with a fork, add a pat of butter and sprinkle with chopped chives or parsley for color.