French Onion Potato Gratin (Printable)

Golden roasted potatoes topped with deeply caramelized onions and bubbling Gruyère cheese.

# What You'll Need:

→ 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)

# Directions:

01 - Preheat oven to 425°F. Line a baking sheet with parchment paper. Toss potato slices in olive oil, kosher salt, and black pepper until evenly coated. Arrange in a single layer on the baking sheet and roast for 25 to 30 minutes, turning halfway through, until golden and tender.
02 - While potatoes roast, heat butter and olive oil in a large skillet over medium-low heat. Add sliced onions and salt, stirring frequently until softened, about 10 minutes. Sprinkle sugar and thyme over onions and continue to cook, stirring occasionally, until deeply caramelized, about 20 to 25 minutes. Adjust heat to prevent burning.
03 - Remove roasted potatoes from oven and layer them in a shallow ovenproof dish or skillet, slightly overlapping. Spread caramelized onions evenly over the potatoes, then top with grated Gruyère cheese.
04 - Return the assembled dish to the oven and bake for 10 to 12 minutes until cheese melts and bubbles. Optionally, broil for an additional 2 to 3 minutes for a golden crust. Garnish with chopped parsley and serve hot.

# Expert Advice:

01 -
  • All the rich, umami depth of French onion soup but as a side dish that actually pairs with dinner instead of stealing the spotlight.
  • The cheese gets bubbly and golden while the potatoes stay creamy inside—it's the textural contrast that makes people ask for seconds.
  • Comes together in just over an hour with mostly hands-off time, so you can prep other things while the magic happens in the oven.
02 -
  • Caramelized onions cannot be rushed—low heat and patience are what separate deep golden flavor from burnt disappointment.
  • Don't crowd the potatoes on the baking sheet or they'll steam instead of roast; give them space to breathe.
  • The cheese needs to be spread over warm (not scorching) potatoes so it melts evenly without the bottom burning.
03 -
  • If your onions start browning too quickly, add a splash of water and scrape up the browned bits—this is flavor, not burning.
  • Don't slice potatoes too thin or they'll shatter; ½-inch is the sweet spot for holding up to roasting and layering.
  • Let the finished dish rest for a few minutes before serving so the layers set slightly and everything stays where you put it on the plate.
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