- 4 large russet potatoes, peeled
- 1 cup clarified butter
- 1/3 cup freshly grated Parmesan cheese, plus additional for garnish
- Kosher salt and freshly ground black pepper
- 1/4 cup crème fraiche
- 3 sprigs fresh thyme, for garnish
- Preheat the oven to 425 degrees.
- Grease a 10-inch cast-iron or heavy nonstick skillet with 3 tablespoons of clarified butter.
- Set the mandoline to 1. Using gentle pressure, carefully slice the potatoes on the mandoline, and place them in a large bowl of ice water. Remove from the water and pat dry with paper towels.
- Brush each potato slice on both sides with clarified butter.
- Heat the greased pan over medium heat. Carefully put 1 slice of potato in the middle of the pan. Arrange the remaining slices around it in overlapping concentric circles to the edge of the pan. Season with salt and pepper and sprinkle with Parmesan cheese. Repeat the process until all the potatoes are used. Remove the pan from the heat.
- Butter a piece of foil and place it buttered side down on top of the potatoes. Using a heavy pan or plate as a weight, press down firmly on the foil to flatten the potatoes. Remove the weight, and cover the pan with a lid or a different piece of foil. Put the pan on a baking sheet to catch any overflow of butter.
- Bake for 30 minutes. Remove from oven and remove cover. Using the same buttered foil and heavy pan as before, once again press down firmly to flatten the potatoes. Return the pan to the oven to bake for another 25 to 30 minutes, until the butter is bubbling and the edges of the potatoes are golden brown.
- Tilt the pan and pour off the excess butter into a heatproof jar or container. Cool for 10 to 15 minutes.
- Loosen the potatoes with a spatula, then carefully flip the potatoes onto a serving platter. Top with crème fraiche, fresh thyme and season with salt and pepper and a sprinkle of Parmesan.