Cover 4 lb. Yukon Gold potatoes, peeled, cut into 2" pieces, 6 large garlic cloves, peeled, and 1 Tbsp. Diamond Crystal or 1¾ tsp. Morton kosher salt with cold water in a large pot. Bring to a low boil on the stovetop over high heat, then reduce heat and simmer (do not boil) until potatoes are very tender when pierced with the tip of a paring knife but not falling apart, 20–25 minutes.

Meanwhile, heat 1¼ cups whole milk, 4 thyme sprigs, and ¾ cup (1½ sticks) unsalted butter in a small saucepan over medium, stirring, until butter is melted. Remove from heat; set aside.

Drain boiled potatoes and garlic; return to pot. Toss over low heat until moisture evaporates, 1–2 minutes. Using potato ricer or food mill, immediately press potatoes and garlic into a large bowl (do not let cool).

Discard thyme from warm milk mixture and gradually stir into hot potatoes, reserving about ½ cup if you plan to make in advance (see Do Ahead). Season with 2 tsp. Diamond Crystal or 1¼ tsp. Morton kosher salt and ¾ tsp. freshly ground black pepper. Fold in ½ cup sour cream and stir with a spoon until incorporated and very smooth (do not overmix or potatoes will become gummy). Taste and adjust seasonings. Serve topped with remaining 2 Tbsp. unsalted butter and more pepper. Do Ahead: Mashed potatoes can be made 2 hours ahead; cover and store at room temperature. Or chill, covered, up to 8 hours; reheat over medium with reserved ½ cup milk mixture, rewarmed to melt butter.

Editor's note: This recipe was first printed November 2016. Head this way for more comfort food favorites →