1. Preheat oven to 375°F (190°C) and lightly grease a 9×13-inch baking dish.

2. In a large deep skillet, melt the butter with the olive oil over medium heat. Add the sliced onions, 1/2 teaspoon of the kosher salt, and the granulated sugar. Cook, stirring often, for 20–25 minutes until deeply golden and caramelized.

3. Stir in the garlic, dried thyme, and black pepper, cooking for about 1 minute until fragrant.

4. Sprinkle the flour over the onions and stir well, cooking for 1–2 minutes to remove the raw flour taste.

5. Pour in the white wine (or extra broth), scraping the bottom of the pan to release any browned bits. Simmer for 1–2 minutes.

6. Slowly whisk in the chicken broth and then the milk, stirring until the sauce is smooth and slightly thickened.

7. Stir in the uncooked orzo, making sure it is submerged, then add the shredded chicken and the remaining 1/2 teaspoon kosher salt. Simmer for about 5 minutes, stirring frequently, until the orzo just starts to soften.

8. Remove the pan from the heat and stir in 3/4 cup of the Gruyère and all of the mozzarella until melted and creamy. Adjust seasoning with additional salt and pepper if needed.

9. Transfer the mixture to the prepared baking dish and spread into an even layer. Top with the remaining 3/4 cup Gruyère cheese.

10. Bake for 20–25 minutes, until the casserole is bubbly around the edges and the orzo is tender.

11. Carefully remove from the oven, sprinkle the crispy French fried onions evenly over the top, and bake for an additional 5 minutes until the onions are lightly toasted.

12. Let the casserole rest for 5–10 minutes, then garnish with fresh parsley and serve warm.