French Onion Potato Gratin (Printable)

Roasted potato slices topped with sweet caramelized onions and bubbling Gruyère cheese.

# Components:

→ Potatoes

01 - 4 large Yukon Gold potatoes, scrubbed and sliced into ½-inch rounds
02 - 2 tablespoons olive oil
03 - ½ teaspoon kosher salt
04 - ¼ teaspoon black pepper

→ Caramelized Onions

05 - 2 large yellow onions, thinly sliced
06 - 2 tablespoons unsalted butter
07 - 1 tablespoon olive oil
08 - ½ teaspoon sugar
09 - ¼ teaspoon salt
10 - 1 teaspoon fresh thyme leaves or ½ teaspoon dried thyme

→ Topping

11 - 1 cup Gruyère cheese, grated (approximately 3.5 ounces)
12 - 2 tablespoons fresh parsley, chopped (optional for garnish)

# Directions:

01 - Preheat the oven to 425°F. Line a baking sheet with parchment paper.
02 - In a large bowl, toss potato slices with olive oil, kosher salt, and black pepper. Arrange the slices in a single layer on the prepared baking sheet. Roast for 25 to 30 minutes, flipping halfway through, until golden and tender.
03 - While potatoes roast, heat unsalted butter and olive oil in a large skillet over medium-low heat. Add sliced onions and salt, cooking while stirring frequently until softened, about 10 minutes. Add sugar and thyme, then continue cooking, stirring occasionally, until deeply golden and caramelized, approximately 20 to 25 minutes. Reduce heat if onions brown too quickly.
04 - Remove roasted potatoes from the oven. Arrange them in a shallow ovenproof baking dish or skillet, slightly overlapping each slice.
05 - Evenly spread the caramelized onions over the potatoes. Sprinkle grated Gruyère cheese on top.
06 - Return the dish to the oven and bake for 10 to 12 minutes until the cheese is melted and bubbling. Optionally, broil for 2 to 3 minutes to achieve a golden brown crust.
07 - Garnish with chopped fresh parsley and serve hot.

# Expert Advice:

01 -
  • It tastes like French onion soup without needing a bowl or spoon, which somehow makes it feel less heavy and more elegant.
  • The caramelized onions do most of the work while your potatoes roast, so you're not actually standing over the stove the whole time.
  • Leftover servings reheat beautifully in a quiet oven, making weeknight dinners feel effortless.
02 -
  • Caramelizing onions truly takes 30–40 minutes of actual cooking time—there's no shortcut that gets you the deep flavor without the time investment.
  • Slicing your potatoes evenly matters more than you'd think; thicker slices won't finish cooking before the cheese browns, leaving you with crunchy centers.
  • Don't skip flipping the potatoes halfway through roasting; it's the difference between golden-on-both-sides and pale-on-one-side.
03 -
  • Have all your ingredients prepped and ready before you start—onion slicing takes longer than you think, and you don't want to be caught scrambling once everything is cooking.
  • Use a cast iron skillet or heavy-bottomed pan for the onions; lighter pans can create hot spots that brown onions unevenly and quickly.
  • Don't skip the broiler step if you like crispy, slightly charred cheese edges—it takes just a few minutes and transforms the texture.
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