The conventional way to cook a roast or thick steak so it develops a well-browned exterior is to sear it over high heat, then finish it the gentler heat of the oven. The reverse-sear method, which we use here, flips the order. We slow-roast a boneless leg of lamb until just shy of perfectly done, then blast it with high heat for browning. It’s an easy, hands-off method that results in meat with more even doneness from edge to center. We toss sliced Yukon Gold potatoes into the roasting pan under the lamb; they soak up the drippings and become an effortless, delicious side. A leave-in thermometer—the type that allows you to remotely monitor the food’s internal temperature as it cooks—is especially handy.