Cheesy Butternut Squash Gratin

Preheat your oven to the desired temperature of 350 degrees Fahrenheit (175 degrees Celsius).

To prevent sticking, lightly coat a 9x13-inch baking dish with non-stick cooking spray.

Melt butter in a large skillet over medium heat. Sauté sliced onions and minced garlic in hot butter until they become soft and golden, taking approximately 10 minutes. Add diced squash and brown sugar to the skillet. Continue cooking and stirring until the squash starts to develop a golden-brown color on its edges, while remaining slightly firm in the center. This process should take around 10 minutes.

Pour the cooked squash mixture into the prepared baking dish, followed by a generous amount of chicken broth. Cover the dish with aluminum foil to retain heat.

Bake the squash mixture in a preheated oven until all liquid has been absorbed and the squash is tender, taking between 45 to 50 minutes.

Simultaneously, combine grated Gruyère cheese, shredded Cheddar cheese, bread crumbs, dried thyme, and fresh rosemary in a medium-sized bowl. Mix the ingredients until they are well-coordinated.

Remove the foil covering from the baking dish and sprinkle the Gruyère mixture evenly across its surface. Add a generous amount of Parmesan cheese on top. Return the dish to the oven and bake, uncovered, until the topping is lightly crunchy and golden-brown, taking approximately 15 minutes.