This is the only way we’re making potatoes from now on.
Active Time::30 mins
Total Time:: 1 hr 25 mins
Servings::8 6- x 4-inch rectangles
Ingredients
3 tablespoons unsalted butter, softened, divided
5 cups thinly sliced yellow onions (1 1/4 pounds total onions)
2 cups heavy whipping cream
2 tablespoons thinly sliced garlic (2 large cloves)
1 1/2 teaspoons fresh thyme leaves, plus more for garnish
1/2 teaspoon chopped fresh rosemary
1/4 teaspoons black pepper
2 1/2 teaspoons kosher salt, divided
2 1/2 pounds medium Yukon Gold potatoes, scrubbed (about 8)
1 1/2 ounces Parmesan, finely shredded, divided (about 2/3 cup)
6 ounces extra-sharp white Cheddar cheese, shredded (about 1 1/2 cups)
Directions
Gather all ingredients. Preheat the oven to 450 degrees F (230 degrees C). Grease the bottom and sides of an 18×13-inch sheet pan with 1 tablespoon of the butter.
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Melt remaining 2 tablespoons butter in a large nonstick skillet over medium. Add onions; cook, covered, stirring occasionally, until onions are soft and translucent, 5 to 7 minutes.
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Reduce heat to medium-low and continue cooking, uncovered, stirring occasionally, until onions become very soft and brown, 30 to 35 minutes. Remove from heat.
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While onions cook, bring cream, garlic, thyme, rosemary, pepper, and 1/2 teaspoon salt to a simmer in a small saucepan over medium; immediately remove from heat.
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Thinly slice potatoes on a mandoline into 1/8-inch-thick rounds.
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Arrange half of the potato slices (about 3 1/2 cups) into a single, overlapping layer on the prepared baking sheet so that bottom of the sheet is not showing.
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Sprinkle evenly with 1 teaspoon salt, caramelized onions, and 1/3 cup Parmesan.
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Top with remaining potato slices in a single overlapping layer, and sprinkle with remaining 1 teaspoon salt.
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Pour hot cream mixture evenly over potatoes. Cover baking sheet tightly with foil.
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Bake in the preheated oven until potatoes are tender when pierced with a fork, 20 to 25 minutes.
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Carefully remove foil, scrape off any potato or garlic slices sticking to it, and sprinkle potatoes with Cheddar and remaining 1/3 cup Parmesan.
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Return to the oven and bake, uncovered, until browned and crusty on top, rotating the pan halfway through, 15 to 20 minutes.
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Sprinkle with more thyme leaves and serve immediately.
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