NYTimes Hasselback Gratin

These potatoes, from J. Kenji Lopez-Alt, got a lot of love and attention when they were published in the NYTimes food section in September 2015. They're the sort of NYTimes recipe that has this kind of comments section, showing the diversity of even the liberal-leaning NYTimes readership:

-- "Oh my goodness, are you trying to kill people with all that fat and starch? This is unconscionable and irresponsible of your publication in 2016!"
-- "If you don't like it, don't make it. Simple. Live and let live."
-- "I'm gluten and dairy free. What can I substitute to make this dairy free? Thoughts?"
-- "This dish is full of dairy. If you don't eat dairy, just make a different dish. Don't ruin this one with substitutions."

And so on.

Sister T. made this to use up some ingredients in her fridge, and, predictably, it was delicious. And it looked cute too.

3 oz finely grated Gruyere or comte cheese
2 oz finey grated Parm-Reg
2 c heavy cream
2 med cloves garlic, minced.
1 T fresh thyme leaves, roughly chopped
salt, pepper
4 -4 1/12 lb russet potatoes, peeled and sliced 1/8 inch thick on a mandoline
    buy extra just in case; depending on potato shape, it may take more or less to fill the dish.
2 T butter

Turn oven to 400 F. Combine cheeses. Transfer 1/3 of cheese mix to separate bowl, set aside. Add cream, garlic and thyme to main cheese mixture. Season generously with salt and pepper. Add potato slices; toss with your hands until every slice is coated with 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 with 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 in this manner, working around the perimeter and into the center until all the potatoes have been added. They should be very tightly packed. If necessary, slice an additional potato, coat with cream mixture, and add to casserole. Pour the excess cream/cheese mixture evenly over the potatoes until the mixture comes halfway up the sides of the casserole. You may not need all the excess liquid and in fact T. didn't; she served the rest heated into a thick gravy on the side and it was scrumptious. (The first time she made it she used all the liquid and it didn't turn out as well).

Cover tightly with foil. Bake for 30 minutes. Remove foil and continue baking until the top is pale golden brown, about 30 more minutes. Remove from oven, sprinkle with remaining cheese, and return to oven. Bake until deep golden brown and crisp on top, about 30 more minutes. Remove from oven, rest for a few minutes, and serve.