• Preheat the oven to 375°F.
• Prepare the squash: Slice the butternut squash in half, scoop out the seeds, peel, and cut into thin half-moons using a sharp knife or mandolin.
  20 ounces butternut squash
• Mix the cream: In a bowl, whisk together the heavy cream, salt, black pepper, nutmeg, and garlic powder until well combined.
  1 cup heavy cream, ½ teaspoon salt, ¼ teaspoon nutmeg, ¼ teaspoon black pepper, ½ teaspoon garlic powder
• Grease the pan: Lightly coat a 2-quart baking dish with olive oil or butter.
  1 tablespoon olive oil
• Layer the squash: Arrange half of the squash slices in the bottom of the dish. Use irregular pieces for the first layer and save the more uniform slices for the top.
• Add cream and cheese: Pour ⅓ of the cream mixture over the squash and sprinkle with some grated Gruyère cheese.
  1 ¼ cup Gruyère cheese
• Repeat layers: Add the remaining squash slices, tucking sage leaves between layers. Pour over the rest of the cream mixture and top with the remaining cheese.
• Bake covered: Cover with foil and bake for 45 minutes.
• Bake uncovered: Remove the foil and bake for another 15 minutes until the top is golden brown and bubbly.

Optional Crispy Sage Topping:

• Melt butter: Heat 1 tablespoon of butter in a skillet over medium heat.
• Crisp the sage: Add 4-5 sage leaves and cook for about 30 seconds per side until crispy.
  5 sage leaves or thyme sprigs
• Drain and serve: Transfer to a paper towel to remove excess oil, then sprinkle over the casserole before serving.