# What You'll Need:
→ Potatoes
01 - 3.3 lbs Yukon Gold or russet potatoes, scrubbed and sliced 1/3 inch thick
02 - 2 tablespoons olive oil
03 - 1/2 teaspoon kosher salt
04 - 1/4 teaspoon freshly ground black pepper
→ Caramelized Onions
05 - 3 large yellow onions, thinly sliced
06 - 2 tablespoons unsalted butter
07 - 1 tablespoon olive oil
08 - 1/2 teaspoon kosher salt
09 - 1 teaspoon fresh thyme leaves or 1/2 teaspoon dried thyme
10 - 1 teaspoon balsamic vinegar
→ Topping
11 - 7 oz Gruyère cheese, grated
12 - 1 oz Parmesan cheese, grated (optional)
13 - 2 tablespoons chopped fresh parsley for garnish
# Method:
01 - Set oven to 425°F and line a large baking sheet with parchment paper.
02 - Toss potato slices with olive oil, kosher salt, and black pepper. Arrange in a single layer on the prepared sheet and roast for 25 to 30 minutes, flipping once halfway, until golden and tender.
03 - While potatoes roast, melt butter with olive oil in a large skillet over medium-low heat. Add sliced onions and salt, stirring frequently for 25 to 30 minutes until deeply caramelized. Stir in thyme and balsamic vinegar and cook 1 to 2 minutes more before removing from heat.
04 - Reduce oven heat to 400°F.
05 - In a lightly greased baking dish, arrange roasted potato slices in a slightly overlapping single layer. Evenly spoon caramelized onions over the potatoes, then sprinkle grated Gruyère and Parmesan (if used) on top.
06 - Bake assembled dish for 10 to 15 minutes until cheese melts and bubbles.
07 - Allow to cool briefly. Garnish with chopped parsley and serve warm.