Scalloped Potatoes with Caramelized Onions and Gruyere

Name: Scalloped Potatoes with Caramelized Onions and Gruyere
Ingredients: 2 tablespoons extra virgin olive oil , divided; 4 cups thinly sliced onions , sliced crosswise; 6 medium Yukon gold potatoes (about 1 1/2 pounds), peeled and sliced 1/8 inch thick (see recipe note); 3/4 cup grated Gruyere cheese , divided; 1/2 cup grated Parmesan cheese; 1 teaspoon kosher salt; 1/2 teaspoon white pepper (or black pepper if that is what you have); 1 teaspoon butter, for greasing the baking dish; 1/3 cup stock (chicken, beef, or vegetable); 1 teaspoon finely minced fresh rosemary