3poundsmedium Yukon Gold potatoescut into 1/8-inch slices
Freshly grated black pepper *SEE NOTE
12ouncesgrated GruyereEmmental, Jarlsburg or Swiss cheese
1cupgrated Parmesan cheese
2tablespoonschopped fresh rosemary or thyme leavesoptional
Line a large, rimmed baking sheet with nonstick cooking spray and heat oven to 450°F.
Heat a large skillet, over medium-low heat, and add the oil and butter. When the oil is hot and butter has melted, add the diced onion. Cook, stirring often, until the onion has softened and is translucent, about 5 minutes.
While the onions cook, scrub, dry and cut the potatoes into 1/8-inch slices. Pat the slices dry with paper towels and lay them (shingle-stylin the prepared baking sheet. The rows of potatoes should barely touch and the potatoes should fill the pan.
Season the potatoes with black pepper, and sprinkle them with half of the Gruyere and half of the Parmesan.
When the onions are ready, raise the heat to medium and add the cream, Dijon and herbs, stirring continuously. Heat just to a simmer and carefully pour the cream/onion mixture over the potatoes. Tilt the sheet pan slightly in all directions to spread the cream/onion mixture to the edges and corners of the pan. Season with additional freshly ground black pepper.
Top with the remaining cheeses; Gruyere first and Parmesan on the very top.
Cover the potatoes with foil that has been sprayed with non-stick cooking spray. Be sure to place the foil sprayed-side down.
Bake 15 minutes at 450°F and remove the foil.
Reduce the temperature to 375°F and continue baking 40-45 minutes or until the potatoes are cooked through, the edges are crispy, the middle is bubbly and the top is golden brown.
Transfer the potatoes from the oven and let cool 15 minutes before serving.
Note: This recipe does not call for salt due to the sodium amounts in the cheeses. If you like things salty, you can add 1 teaspoon kosher salt when adding pepper.