Potatoes are delicious, but they sometimes feel sort of frumpy and old-fashioned. Not these potatoes! Scalloped potatoes are elegant — the wafer-thin slices suffused with flavor, the delicate layers reminiscent of pastry. Yet, impressive as they are, scalloped potatoes are easy to prepare, and this version, which includes Gruyere and ham, is substantial enough to serve as a main course.
Some gratin recipes begin with a bechamel — a stove-top sauce made from flour, butter and cheese — but I’ve found that the potatoes have ample starch to hold the dish together as long as you use a wide, shallow baking dish. There’s a French potato dish, gratin dauphinois, that adds a subtle garlic flavor by rubbing the baking dish with garlic, and I’ve added that technique here for a hint of garlic flavor.
Heat oven to 350 degrees Fahrenheit (177 degrees Celsius). Rub ½ tablespoon of the butter over the sides and bottom of a 9-by-13-inch (33-by-23 cm) baking dish, coating thoroughly. Follow with the garlic halves, running the cut side over the entire surface of the dish.
Peel and slice the potatoes as thinly as possible. Spread about one-third of the slices over the bottom of the prepared baking dish, overlapping edges slightly, like fish scales.
Sprinkle potato layer with ½ teaspoon salt, ¼ teaspoon black pepper, ½ tablespoon rosemary, ½ cup cheese and one-third of the ham (about ½ cup).
Repeat two more times, creating three even layers. Pour in half and half. It should come up almost to the top, but not cover the final layer. If it doesn't, you can add another tablespoon or two.
Bake for 1 hour. Rest for 10 to 15 minutes before serving.
Pro tip: This gratin is lovely with almost any cheese. Try replacing the Gruyere with cheddar, Parmesan, or Gouda.