Instructions

1. Arrange a rack in the middle of the oven and heat the oven to 375ºF. Meanwhile, pressure cook the potatoes.
2. Measure 1 cup water in a liquid measuring cup. Mince 6 garlic cloves. Add the garlic, 1 teaspoon of the kosher salt, 1/2 teaspoon black pepper, and 1/2 teaspoon dried thyme to the water. Grate 8 ounces cheese on the large holes of a box grater (about 2 packed cups).
3. Peel 2 pounds russet potatoes. If using a mandoline, place it over a 6-quart or larger Instant Pot or electric pressure cooker. Cut the potatoes crosswise into 1/4-inch thick rounds directly into the pressure cooker. If using a knife, cut the potatoes crosswise into 1/4-inch thick slices and transfer to the pressure cooker. Add the water mixture and stir to combine.
4. Lock the lid on and make sure the valve is set to seal. Set to cook under HIGH pressure for for 1 minute. It will take 10 to 12 minutes to come up to pressure.
5. When the cook time is up, quick release the pressure. Using a slotted spoon, transfer the potatoes to an 8x8-inch or other 1-quart broiler-safe baking dish (a few slices of potato left behind in the insert is okay).
6. Turn on the highest Sauté function on the pressure cooker. Add 2 tablespoons unsalted butter to the potato cooking liquid. Once the butter melts, add 2/3 cup heavy cream or half-and-half and bring to a simmer.
7. Add 1 cup of the cheese, 1/4 teaspoon grated nutmeg, and the remaining 1/4 teaspoon kosher salt. Whisk to combine and cook until the cheese is melted and the sauce is creamy, about 2 minutes. Pour over the potatoes and gently mix to combine, making sure the sauce gets in between the potato slices. Sprinkle evenly with the remaining cheese.
8. Bake until the cheese on top is melted and the potatoes are tender, about 5 minutes. Turn the oven to broil. Broil until the cheese is deeply browned, 5 to 7 minutes. Let cool 5 minutes for the sauce to thicken before serving. Garnish with finely chopped chives if desired.