French onion potato gratin (View Print Version)

Roasted potato slices with deeply caramelized onions and melted Gruyère for a flavorful side dish.

# What You'll Need:

→ Potatoes

01 - 4 large Yukon Gold potatoes, scrubbed and sliced into 1/2-inch rounds
02 - 2 tablespoons olive oil
03 - 1/2 teaspoon kosher salt
04 - 1/4 teaspoon black pepper

→ Caramelized Onions

05 - 2 large yellow onions, thinly sliced
06 - 2 tablespoons unsalted butter
07 - 1 tablespoon olive oil
08 - 1/2 teaspoon sugar
09 - 1/4 teaspoon salt
10 - 1 teaspoon fresh thyme leaves or 1/2 teaspoon dried thyme

→ Topping

11 - 1 cup (100 grams) Gruyère cheese, grated
12 - 2 tablespoons fresh parsley, chopped (optional)

# Method:

01 - Preheat the oven to 425°F. Line a baking sheet with parchment paper. Toss potato slices with olive oil, kosher salt, and black pepper, then spread them evenly on the baking sheet in a single layer.
02 - Roast the potato slices for 25 to 30 minutes, flipping halfway through, until they are golden brown and tender.
03 - While the potatoes roast, heat butter and olive oil in a large skillet over medium-low heat. Add sliced onions and salt, cooking and stirring frequently until soft, about 10 minutes. Add sugar and thyme, continue cooking, stirring occasionally, until onions turn a deep golden brown, approximately 20 to 25 minutes. Lower heat if onions begin to brown too quickly.
04 - Remove roasted potatoes from the oven and arrange them in a shallow baking dish or ovenproof skillet, overlapping the slices slightly.
05 - Evenly spread the caramelized onions over the potatoes, then sprinkle the grated Gruyère cheese over the top.
06 - Return the dish to the oven and bake for 10 to 12 minutes until the cheese melts and bubbles. Optionally broil for 2 to 3 minutes to achieve extra browning.
07 - Garnish with chopped fresh parsley if desired and serve immediately while hot.

# Expert Advice:

01 -
  • The cheese gets all bubbly and bronzed while the potatoes stay tender inside with crispy edges.
  • Once you master caramelized onions, you'll find yourself making this on repeat because it feels fancy but honestly requires just patience and a pan.
  • It's naturally vegetarian and gluten-free, which means more people get to enjoy it without fuss.
02 -
  • The biggest mistake is cooking onions too fast—if you crank up the heat, they'll burn on the outside before they soften inside, and no amount of time will fix that.
  • Don't overlap your potato slices too much or they'll steam instead of roast; give them space for air to circulate and edges to crisp up.
03 -
  • A splash of dry white wine or even sherry stirred into the onions during the last few minutes of cooking adds a subtle sophistication that makes people ask what your secret ingredient is.
  • If you have an ovenproof skillet instead of a baking dish, cook everything in that from start to finish—one less pan to wash and everything stays hotter longer.
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