Butternut Squash Gratin

Preheat your oven to 400°F (200°C) and lightly grease a 2-quart baking dish with butter or non-stick spray.
In a large bowl, toss the sliced butternut squash with the olive oil, 1/2 teaspoon of the salt, and the black pepper until the slices are evenly coated.
Arrange the seasoned squash slices in overlapping rows in the prepared baking dish, creating an even layer.
In a medium bowl, whisk together the heavy cream, minced garlic, remaining 1/2 teaspoon of salt, and nutmeg. Pour this cream mixture evenly over the squash in the baking dish.
Sprinkle 1 cup of the shredded Gruyère cheese and all of the Parmesan cheese evenly over the squash and cream.
In a small bowl, combine the remaining 1/2 cup of Gruyère cheese, the panko bread crumbs, and the melted butter. Sprinkle this breadcrumb topping evenly over the gratin.
Cover the baking dish with aluminum foil and bake for 30 minutes. Then, remove the foil and continue baking for another 20-25 minutes, or until the squash is tender when pierced with a fork and the top is golden brown and bubbly.
Let the gratin rest for 10 minutes before serving to allow the sauce to thicken slightly.