When Chantal and I first started dating, we did not have the money to go out. A steak and these potatoes was a favorite meal. We cooked the potatoes in our first joint purchase, a nonstick pan. At L'Auberge de L'Ill we served the potatoes, larded with truffles, with a New York strip steak. It's a shredded potato pancake, very crisp on the outside and soft inside. The name, paillasson, refers to its spiky, flat look; a paillasse is a straw mattress or doormat. Serve the potatoes with a dish with sauce so they can soak it up and as a side dish to fried eggs.
Note: Cutting the potatoes on a mandoline gives a spikier, more paillasson look to your cake. But the coarse blade of a food processor is also fast and easy. You can also make this dish with a combination of parsnip and potato.
If you want to add some black or white truffle, chop it and toss with the potatoes. You could also sprinkle the finished cake with truffle salt or truffle oil. Adding herbs is a colorful and nice addition. Thyme is always appropriate, and Chantal and I both love minced rosemary in these potatoes. You could top the cake with smoked salt and a dollop of crème fraîche, too.
I make this dish with butter or a combination of butter and oil, but you can use all olive oil.
Cut the potatoes into a fine julienne with a mandoline or with the coarse shredding blade of a food processor. (Once they are grated, do not rinse the potatoes; you need their starch to hold the potatoes together.)
Transfer them to a baking sheet, season well with salt and pepper, and let sit for a few minutes. Place the sheet on a tilt; the salt will begin to wilt the potatoes and they will begin releasing water.
Heat 1 tablespoon of the butter and 1 tablespoon of the oil in a 9- or 10-inch nonstick skillet over medium heat. Squeeze the potatoes very hard between your hands to remove as much water as possible and then add them to the pan. With the back of a large spoon, neaten the edges and lightly press the potatoes to make a flat cake.
Cook for a few minutes and then rub all around the edge of the pan with a tablespoon-sized nut of butter so that it melts and runs under the potatoes.
Cook over medium heat until crispy and brown, about 10 minutes. Slide the cake carefully out onto a plate, cover it with a second plate, add another piece of butter to the pan, and then invert the plates and slide the cake back into the pan to cook the second side.
Cook, adding butter or oil as needed around the edges and tilting the pan, until the cake is crispy underneath and the potatoes have cooked through, 7-10 more minutes. Regulate the heat so the cake browns and caramelizes but does not burn.
Slide it onto a cutting board, blot any excess oil with paper towels, cut into 8 wedges with a sharp knife, and transfer to a large round serving platter. Season with salt, to taste, and serve immediately.