-
Position rack in middle of oven. Preheat the oven to 400°F/200°C. Use butter to coat the inside of a 3-quart (2.8 L) shallow casserole dish and set aside.
-
Cut the potatoes into very thin 1/8-inch (3 mm) slices using a very sharp knife or a mandoline (see Tips). Keep them in rounds, if possible.
-
Place the potatoes in a wide heavy saucepan (I use a 3-quart/2.8 L) and add the half-and-half, salt, a generous amount of pepper and thyme and/or nutmeg, if using. Bring to a vigorous simmer over medium heat, shaking the pan occasionally, and simmer for 3 minutes.
-
Carefully pour the mixture into prepared casserole dish. Use a silicone spatula to gently coax the potatoes and liquid into an even layer. Sprinkle the cheese evenly over the top.
-
Bake for about 35 to 45 minutes or until the potatoes are tender when pierced with a knife and the top is golden and bubbling. The mixture might look a little loose, but don’t worry, it will firm up upon cooling. Place casserole on a rack and cool for at least 15 minutes to allow the gratin to achieve its maximum potato perfection. Serve warm or even at room temperature.