Potato Gratin Fries

I really, really want a deep fryer. These would be really, really good. From the Washington Post Magazine, August 23, 2015.

Potato Gratin Fries

A rich, special-occasion dish of beautifully layered potatoes, crisp on the outside and buttery within. Without the top crust, it's not a true gratin, but it is assembled in the same way for the baking. At G by Mike Isabella, these accompany a cauliflower "steak"; you can serve them the same way you would any fries: alongside roasts or steaks, with sandwiches or salads, or as an appetizer (with ketchup or the dipping sauce of your choice, if desired). You'll need an instant-read thermometer.

Make Ahead: The baked potato gratin needs to be refrigerated/weighted overnight. It can be refrigerated for up to 5 days before frying.

Servings: 12-16
Tested size: 12-16 servings

Ingredients

• 5 pounds russet potatoes (5 to 6 large), peeled
• 16 tablespoons (2 sticks) unsalted butter, melted
• 1 tablespoon coarse sea salt
• Vegetable oil, for frying

Directions 

1. Preheat the oven to 350 degrees. Slice the potatoes as thinly as possible, preferably using a mandoline. (Don’t worry about immersing them in water to keep them from turning gray; the last-step frying renders that moot.)
2. Line the bottom of an 8-inch square baking dish with parchment paper, and brush it with some of the melted butter. Arrange one layer of the potatoes in the dish, overlapping them slightly. Brush with the butter and sprinkle with a little bit of the salt. Repeat with another layer of potatoes, butter and salt, and repeat until all the potatoes, butter and salt are used.
3. Cover the dish tightly with aluminum foil; bake until the potatoes are tender when pierced with a skewer, 60 to 90 minutes. Remove from the oven. Fit a dish on top so it presses directly on the potatoes through the foil, and put a few heavy cans of tomatoes or beans on the dish, as weights. Cool to room temperature, then transfer the setup to the refrigerator to chill and compress overnight.
4. When ready to fry, pour the oil to a depth of 4 inches into a deep skillet over medium-high heat. Set a cooling rack over a baking sheet lined with paper towels.
5. Remove the potato gratin from the refrigerator. Fill the sink with an inch of hot tap water, and set the pan in the water for a minute or two to loosen the solid mass. Discard the foil, run a knife blade around the inside edge of the dish and invert onto a cutting board so the gratin comes out in one block. Discard the parchment paper.
6. Use a sharp knife to cut the gratin into 1-inch slabs. Turn each slab onto its side and cut on the diagonal into 1/2-inch pieces. Return the bulk of the pieces to the refrigerator to stay chilled until you fry them.
7. Once the oil registers 375 degrees on an instant-read thermometer, use a slotted spoon to carefully lower each piece into the hot oil, holding it for a few seconds before releasing (so the layers won't break up). Fry in batches, to avoid overcrowding, until the potatoes are golden brown, about 5 minutes. (Fry any odd/stray layered potato pieces left over from cutting, too.) Transfer to the cooling rack. Serve warm.