Acclaimed food science writer, J. Kenji López-Alt has developed this sort of “mash-up ” ( if you will ) of a classic French gratin, and a beautiful Hassleback potato recipe. The idea is to stand the slices of potato vertically, rather than laying them flat. This ensures each serving receives both a creamy potato serving and a crispy edge in each bite.
This is my adaption.
4 to 4 ½ pounds russet potatoes, peeled and sliced 1/8-inch thick slices with a sharp knife of on a mandoline
4 tablespoons unsalted butter
1 1/2 cups heavy cream
1/2 cup chicken stock
3 medium cloves garlic, minced
1 tablespoon fresh thyme, leaves removed for the stem
Kosher salt and black pepper
1/4 teaspoon ground white pepper
1/2 teaspoon red chili flakes
2 cups finely grated Gruyère cheese
1/2 cup finely grated Parmigiano-Reggiano
1 bunch chives, chopped for garnish
Adjust oven rack to middle position and heat oven to 400’F degrees. Combine cheeses in a large bowl. Transfer 1/3 of cheese mixture to a separate bowl and set aside for garnish.
Add cream, stock, garlic and thyme to the cheese mixture, and mix well. Season with salt and pepper, add white pepper, and red chili flakes– stir to combine.
Add potato slices and 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.
Prepare a 2-quart casserole dish with butter. Place on a high sided baking sheet.
Pick up a handful of potatoes, organizing them into a neat deck stack, 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 with cream mixture, and add to casserole. It is important the potatoes are very tight.
Pour the excess cheese mixture evenly over the top of the potatoes in the casserole dish until the mixture comes halfway up the sides. You may not need all the excess liquid.
Cover dish tightly with foil– sprayed on the inside with non-stick cooking spray. Transfer to the oven. Bake for 30-40 minutes. Remove foil and continue baking until the top is golden brown, about 45 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, garnish with chopped chives and serve.