Ingredients:

  • 2 medium (about 3.5 lbs) Butternut Squash, peeled, seeded, and sliced 1/8 inch thick
  • 7 Tbsp Unsalted Butter, divided
  • 1/4 cup All-Purpose Flour
  • 1 cup Whole Milk, warmed
  • 1 cup Heavy Cream
  • 2 cups Freshly Grated Gruyère Cheese, divided
  • 1 tsp Salt
  • 1/2 tsp Black Pepper, freshly cracked
  • 1/4 tsp Freshly Grated Nutmeg
  • 1 tsp Fresh Thyme, chopped
  • 12 large Fresh Sage Leaves
  • 1 cup Panko Breadcrumbs

Instructions:

  1. Preheat oven to 375°F (190°C). Lightly grease a 9x13 inch casserole dish. Prepare the butternut squash by peeling, scooping out the seeds, and slicing it into very thin, uniform rounds or half-moons (about 1/8 inch or 3 mm thick). Set aside.
  2. Make the Béchamel: In a medium saucepan, melt 4 Tbsp of the butter over medium heat. Whisk in the flour and cook, stirring constantly, for 1 minute to form a roux.
  3. Gradually whisk in the warm milk and cream until the mixture is smooth and thickened (about 3-4 minutes). Ensure there are no lumps.
  4. Remove the sauce from the heat. Stir in 1 1/2 cups of the Gruyère cheese, salt, pepper, nutmeg, and thyme until the cheese is fully melted and the sauce is homogenous. Taste and adjust seasoning.
  5. Assemble the Gratin: In a large bowl, pour about 1/4 cup of the béchamel mixture over the sliced squash and toss gently to coat all slices. Arrange the remaining squash slices snugly, overlapping them slightly, in the prepared casserole dish. Pour the remaining béchamel sauce evenly over the layered squash.
  6. Initial Bake: Cover the casserole dish tightly with foil. Bake for 40 minutes at 375°F (190°C).
  7. Prepare the Crispy Sage Crumble: While the gratin bakes, melt the remaining 3 Tbsp butter in a small skillet over medium heat. Add the whole sage leaves and cook until they crisp up (about 1 minute); remove them and set aside. Keep the sage-infused butter in the pan.
  8. Add the Panko breadcrumbs to the sage butter and toast, stirring constantly, until golden brown (about 2-3 minutes). Remove from heat immediately. Roughly chop the crispy sage leaves and stir them into the Panko mixture.
  9. Finish Baking: After the initial 40 minutes, remove the foil. Sprinkle the remaining 1/2 cup of Gruyère cheese over the top, followed by the crispy sage crumble mixture. Return the gratin to the oven, uncovered, and bake for an additional 15–20 minutes, or until the topping is golden brown, bubbly, and the squash is completely fork-tender.
  10. Let the gratin rest for 10 minutes before serving, allowing the sauce to set.