For the ingredients, I went to Trader Joe's: a 2-lb. bag of small Yukon Gold potatoes, a pint of half-and-half, and a chunk of their best Gruyère. I rubbed my oval baking dish with butter and a clove of garlic. Then I scrubbed the potatoes and sliced them into very thin rounds with my V-slicer. It's fun. (You may prefer the fancier mandoline, but a Japanese V-slicer is equally effective, fast, safe, and at least $100 cheaper.)
Put the potatoes in a medium saucepan with the half-and-half and add salt, pepper, and ground nutmeg. Simmer gently until the potatoes have softened. Grate the cheese as you're waiting. You should have about two cups, but more is better, of course.
If you want to enrich the flavor, you can sauté a small amount of thinly sliced and chopped sweet onion in a little butter and add it to the pot. But the three-ingredient version is a winner.
Spoon the mixture into the baking dish, alternating with sprinklings of cheese as well as more dashes of nutmeg, salt, and pepper to taste. Pour the last of the liquid around the dish. Save plenty of cheese to cover the top. I also added a layer of panko (Japanse bread crumbs) for extra crispness.
Bake at 425° for 30 to 40 minutes, or until the top is golden-brown and gorgeous. Or bake longer at lower heat if you've got other dishes in the oven. Serves 6 to 8 hungry eaters and reheats nicely. I can't wait to make it again, and next time I'll have my camera on hand.