- Place the diced potatoes in a large saucepan of generously salted cold water and bring to a boil, uncovered, over high heat. Reduce the heat to medium-high and simmer until the potatoes are fork-tender, about 20 minutes. Drain the potatoes in a colander.
- Add the butter to the saucepan in which you boiled the potatoes (the heat of the pan will melt it) but do not return to the stovetop. Press the potatoes through a ricer directly into the pot. Return the saucepan to low heat and stir in the sour cream and milk until smooth. Stir in the green onions and season to taste with salt and pepper. Serve immediately.
Make Ahead Tip: Mashed potatoes can be tricky to make in advance, but here’s a tip from my restaurant days. Peel and dice the potatoes the evening before and chill, covered, in a bowl of water with a pinch of salt. Up to 1 hour before serving time, drain and boil the potatoes in fresh water and prepare as above. Transfer the mashed potatoes to a metal bowl, cover tightly with plastic and place over a saucepan filled with 2 inches (5 cm) of water over medium-low heat. The steam from the water below will keep the potatoes hot. Stir the potatoes well, transfer to a serving dish and bring to the table.
From Set for the Holidays with Anna Olson, Appetite by Random House, 2018.