Preparation

• 烤箱架调整到中间位置和公关eheat the oven to 400°F. Combine the cheeses in a large bowl. Transfer 1/3 of the cheese mixture to a separate bowl and set aside. Add the cream, garlic, and thyme to the cheese mixture. Season generously with salt and pepper. Add the potato slices and toss with your hands until every slice is coated with the cream mixture, making sure to separate any slices that are sticking together to get the cream mixture in between them.
• Grease a 2-quart casserole dish with the butter. Pick up a handful of potatoes, organizing them into a neat stack, and lay them in the casserole dish with their edges aligned vertically. Continue placing potatoes in the dish, working around the perimeter and into the center until all the potatoes have been added. The potatoes should be very tightly packed. If necessary, slice an additional potato, coat it with the cream mixture, and add it to the casserole. Pour the excess cheese/cream mixture evenly over the potatoes until the mixture comes halfway up the sides of the casserole. You may not need all the excess liquid.
• Cover the dish tightly with foil and transfer to the oven. Bake for 30 minutes. Remove the foil and continue baking until the top is pale golden brown, about 30 minutes longer. Carefully remove from the oven, sprinkle with the remaining cheese, and return to the oven. Bake until deep golden brown and crisp on top, about 30 minutes longer. Remove from the oven, let rest for a few minutes, and serve.