The Fluffiest Mashed Potatoes

Fill a large pot halfway with cold water. Peel 4 pounds russet and 1 pound Yukon Gold potatoes and cut into 2" pieces, adding to pot as they are cut. Add cold water to cover by 1" if needed. Stir in 3 tablespoons kosher salt. Bring to a boil, then reduce heat to medium-low and gently simmer until tender, 10-15 minutes. Drain potatoes and transfer to a baking sheet. Let dry, 5-10 minutes.

Meanwhile, heat 1 cup whole milk, 1/2 cup heavy cream, 8 whole black peppercorns, 3 sprigs thyme or 1 sprig rosemary, and 2 bay leaves in a small saucepan over medium heat, stirring occasionally, until mixture is very hot but not boiling, about 10 minutes. Remove from heat and let mixture infuse for 20 minutes; strain. This will add herbal flavor without coloring the liquid.

Pass potatoes through the smallest disk of a food mill along with 1/2 cup (1 stick) cubed, chilled unsalted butter into a large bowl. Stir in the hot cream mixture. Season generously to taste with kosher salt and freshly ground black pepper. To hold, press plastic wrap directly against the surface and set bowl over (not in) a large pot of simmering water for up to 2 hours.