Preheat oven to 400 degrees Fahrenheit.

Slice the potatoes thin using a mandoline or sharp knife. Grease a nine-inch round or square baking dish with butter.

Arrange the potatoes vertically in the dish, alternating colors. 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 your slices are extremely thin, put two together so you see each color.

Mix the two cheeses in a large bowl. Transfer one-third of the cheese mixture to a separate bowl and set aside. Add cream, garlic and herbs to cheese mixture. Season generously with salt and pepper. Pour the cream and cheese mixture evenly over the potatoes until the mixture comes halfway up the sides of the casserole.

Cover dish tightly with foil and transfer to the oven. Bake for 45 minutes. Remove foil and continue baking until the top is pale golden brown, about 30 minutes longer.

Carefully remove from oven, sprinkle with remaining cheese, and return to oven. Bake until deep golden brown and crisp on top, about 30 minutes longer.

Remove from oven, let rest for a few minutes, and serve.