Ingredients
2 tablespoons extra virgin olive oil
4 cups thinly sliced onions (sliced crosswise, see how to cut the onions)
6 medium to small Yukon Gold potatoes (about 1 1/2 pounds), peeled and thinly sliced (1/8 inch thick, helps use a mandolin)
3/4 cup grated Gruyere, divided 1/2 cup, 1/4 cup
1/2 cup grated Parmesan
1 teaspoon of salt
1/2 teaspoon white pepper (or black pepper if that's what you have)
1 teaspoon of butter to butter the gratin or casserole dish
1/3 cup broth (chicken, beef or vegetable broth, use vegetable broth for the vegetarian option)
1 teaspoon finely chopped fresh rosemary
METHOD
1 Sauté the onions until golden brown: heat 1 tablespoon of olive oil over medium-high heat in a heavy-based sauté pan. Add the sliced onions, toss to coat with olive oil and cook until golden, about 15 to 20 minutes.
2 Preheat the oven to 400 ° F (205 ° C).
3 Mix the sliced potatoes with the olive oil, cheese, salt, pepper: In a large bowl, put the sliced potatoes and mix gently with 1 tablespoon of olive oil. olive, 1/2 cup grated Gruyere, 1/2 cup grated Parmesan, salt, and white pepper.
(If you are making ahead, make sure the potatoes are well coated with olive oil, even if you need to add more olive oil. This will prevent them from turning gray.)
4 Spread the onions in a buttered dish, place the potatoes on top, pour the broth, sprinkle with cheese: Lightly butter a large gratin dish or a 9x13 casserole dish and line with the caramelized onions in an even layer at the bottom of the dish.
Arrange sliced potatoes (including grated cheese) in a pattern over onions.
Pour the broth over the potatoes. Sprinkle with the rest of the cheese.
5 Cover with foil and bake, then broil to finish: Cover with foil and bake at 400 ° F (205 ° C) for 50 minutes (or until fork is tender). Remove the foil. Grill for 5 minutes, uncovered, until lightly browned.
Sprinkle with chopped rosemary to serve.
from Simply Recipes ~ https://www.simplyrecipes.com/recipes/scalloped_potatoes_with_caramelized_onions_and_gruyere/