Why It Works
- By arranging the potatoes accordion-style, just like with Hasselback roasted potatoes, you get an ultra-crispy top with a creamy, tender center.
- Tossing the potato slices with the cream and cheeses first guarantees an even distribution in the baking dish, and helps the potatoes reach the perfect texture.
You've probably seen Hasselback potatoes before. They've definitely had their moment of being a full-on viral recipe trend among food blogs, Instagram feeds, and mainstream media. According to some unsourced online references, the dish was created at the Hasselback restaurant in Stockholm sometime in the 18th century (this was way before the Internet started bacon-ing everything).
At their simplest, Hasselback potatoes are made by slicing potatoes at regular intervals almost all the way through, then separating the ridges, adding a bit of butter or oil in between the ridges, and baking them until they're crisp and creamy. They come out looking like, well, like nothing else I can really think of. Dragon's eggs? Bad guys in a Super Mario game? Point is, they look awesome.
But, to be absolutely honest, I've never been too happy with the way they taste. They're supposed to combine the best part of a baked potato—the creamy, moist interior—with the best part of roasted potato chunks—the crispy edges—but really, they produce only mediocre versions of both. The interior is never as moist as I want it, and the edges are always more dried and leathery than really crisp.
The main problem is that, because of all the slits, a Hasselback potato loses lots of moisture as it bakes. The interior ends up drying out unnecessarily. At the same time, the ridges on top don't crisp as well as they should because, in order to get truly crisp edges, like in a French fry or a good roast potato, you need to first gelatinize the starch inside the potato to form a continuous structure. This requires moisture.
I spent a few dozen batches' worth of potatoes trying to fix these deficits before I woke up in the middle of a Tuesday night with an idea, and I couldn't go back to sleep. I went into the kitchen and got to work on the first batch of what would end up being my favorite potato recipe in years.
Here's the thought: What if I were to take the creamy interior and the crisp edges to the extreme, combining the concept of a Hasselback potato—that array of crisp ridges at the top—with a creamy potato gratin, the king of all casseroles?
It'd be a sideways potato gratin, if you will.
The concept of a Hasselback potato, with the ridges all cut into a single intact potato, is neat, but it's not particularly practical. Nor, as it turns out, is it the optimal way to get the crispiest edges in your dish. What we really want is to stack together many slices of potato that vary in size, so as to create plenty of bits that stick in and out. More surface area for better crisping. As a bonus, this also greatly reduces the amount of fiddly prep work required.
The dish starts out just like most potato gratins: with sliced potatoes. If you've got an inexpensive mandoline slicer, then it's a snap. I tried it with both peeled and unpeeled potatoes and preferred the cleaner crunch you get from peeled potatoes.
From there, it progresses like a standard gratin: I mix heavy cream, grated cheese (I used Comté and Parmesan), chopped thyme leaves, salt, and pepper in a bowl. (About a cup of cream per pound of potatoes works well.)
Then I add the potatoes and toss them all together. This step is worth taking your time with: It's crucial that every single potato slice gets coated on all sides with the mixture. That means prying or sliding apart all the slices of potato that are stuck together and dipping them into the cream mixture.
That cream not only adds flavor and moisture but also keeps the potato slices from sticking together as they cook. Without it, the starches released when the potatoes are sliced will swell up, sucking up extra moisture and turning the interior of the casserole gluey and starchy instead of creamy and tender.
Here's where we turn things on their side: Rather than stacking the sliced potatoes horizontally, as in a traditional gratin, I pack them into a greased baking dish standing on their edges, working my way around the perimeter of the dish and packing it all in tightly. Because potatoes vary wildly in exact shape, you end up with tons of little nubby bits sticking out all over the top surface.
Nubby bits that will crisp up as they cook.
To get the interior extra creamy and moist, I add all the excess cream/cheese mixture to the baking dish. Your potatoes should end up about half submerged, with a few stray pieces of cheese and thyme strewn across the top.
So what's the trick to getting the top crisp instead of leathery? Well, the coating of fat helps, for starters. It prevents excess evaporation of moisture, which allows the starchy potato slices to partially gelatinize before they dry out fully. But I found that, for optimum crisp-tender texture, I needed to adopt a two-stage cooking process, similar to how I cook my ultra-crispy roast potatoes.
I start out baking the gratin covered in foil, so that trapped moisture steams the potatoes until they're tender, followed by a good cook uncovered to dry and brown them.
As the potatoes cook, the cream eventually starts to boil, simmering up and over the tops of the potatoes, basting them as they roast, aiding further in preventing them from getting leathery.
Another layer of cheese, added halfway through the uncovered portion of the cook, adds a layer of flavor to the gratin.
During the last stages of cooking, the cream eventually loses enough moisture that it breaks, releasing its butterfat, which coats and then gets slowly absorbed into the potatoes as they continue to lose water content. Milk proteins in the cream and the cheese coagulate, creating little pockets of curd-like tenderness between slices.
The final dish is nothing short of glorious. Every bite has a combination of crisp but moist upper potato ridges and rich and creamy potatoes underneath, with cheese underscoring the whole affair.
3 ounces (85g) finely grated Gruyère or Comté cheese
2 ounces (60g) finely grated Parmigiano-Reggiano cheese
2 cups (480ml) heavy cream
1 tablespoon fresh thyme leaves, roughly chopped
2 medium cloves garlic, minced
Kosher salt and freshly ground black pepper
3 to 3 1/2 pounds (1.4 to 1.6kg) russet potatoes, peeled and sliced 1/8 inch thick on a mandoline slicer (5 to 6 medium potatoes; see note)
2 tablespoons (30g) unsalted butter
Adjust oven rack to middle position and preheat oven to 400°F. Grease a 2-quart baking dish with butter. Combine cheeses in a large bowl. Transfer 1/3 of cheese mixture to a separate bowl and set aside. Add cream, thyme, and garlic to cheese mixture. Season generously with salt and pepper. Add potato slices and toss with 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.
Pick up a handful of potatoes, organizing them into a neat stack, and lay them in prepared baking dish with their edges aligned vertically. Continue placing potatoes in dish, working around the perimeter and into the center until all potatoes have been added. Potatoes should be very tightly packed. If necessary, slice additional potatoes, coat slices with cream mixture, and add to dish (see note). Pour excess cream/cheese mixture evenly over potatoes until mixture comes halfway up sides of dish. You may not need all excess liquid (see note).
Cover tightly with foil and transfer to oven. Bake for 30 minutes. Remove foil and continue baking until 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.
Because of variation in the shape of the potatoes, the amount of potato that will fit into a single baking dish varies. Longer, thinner potatoes will fill a dish more thoroughly than shorter, rounder potatoes. When purchasing potatoes, buy a few extra in order to fill the dish if necessary. Depending on the exact shape and size of the potatoes and baking dish, you may not need all of the cream mixture.
How to Scale Down This Recipe to Feed a Smaller Crowd
This recipe can be scaled by half. Divide all ingredients by two; substitute a 10-inch skillet for the baking dish listed.