Ingredients:

  • 3 lbs (approx. 2 medium) Butternut Squash, peeled, seeded, sliced 1/8 inch thick
  • 1 tsp Kosher Salt, plus extra for seasoning
  • 1/2 tsp Black Pepper, freshly ground
  • 1 Tbsp Olive Oil
  • 4 Tbsp Unsalted Butter, cut into pieces (for béchamel)
  • 10 large Fresh Sage Leaves, finely chopped
  • 4 Tbsp All-Purpose Flour
  • 1 cup Whole Milk, warmed slightly
  • 1 cup Heavy Cream, warmed slightly
  • Pinch Fresh Nutmeg, grated
  • Salt and White Pepper, to taste
  • 5 oz Gruyère Cheese, freshly grated
  • 1/2 cup Panko Breadcrumbs
  • 1 Tbsp Unsalted Butter, melted (for topping)

Instructions:

  1. Preheat the oven to 375°F (190°C). Lightly grease a 9x13 inch casserole dish with butter.
  2. Peel and seed the butternut squash. Using a mandoline or sharp knife, slice the squash into even, thin rounds (approx. 1/8 inch or 3 mm). Uniformity is key for even cooking.
  3. In a large bowl, toss the sliced squash with 1 tablespoon of olive oil, kosher salt, and black pepper. Set aside.
  4. Melt the 4 Tbsp (57g) of butter in a saucepan over medium heat. Add the chopped sage and cook for 1 minute until fragrant (do not let the sage crisp).
  5. Whisk in the flour and cook, stirring constantly, for 2 minutes—this removes the raw flour taste. This is your roux.
  6. Slowly whisk the warmed milk into the roux, a splash at a time, until the sauce is smooth and lump-free. Once smooth, pour in the heavy cream and continue to cook, stirring, until the sauce thickens enough to coat the back of a spoon (about 5-7 minutes).
  7. Remove the sauce from the heat. Stir in the nutmeg, salt, and white pepper. Taste and adjust seasoning—it should be slightly salty as the squash will absorb some of it.
  8. Pour a thin layer of béchamel sauce (about 1/4 of the total sauce) into the bottom of the prepared casserole dish.
  9. Overlap the seasoned squash slices slightly in tidy, tight rows, covering the base of the dish.
  10. Spoon another half of the remaining sauce over the squash layer. Add a second layer of squash, then finish with the remaining béchamel.
  11. In a small bowl, toss the grated Gruyère with the Panko breadcrumbs and the melted butter. Sprinkle this mixture evenly over the top layer of sauce.
  12. Cover the casserole dish tightly with foil. Bake for 30 minutes. This step allows the squash to steam and soften fully.
  13. Remove the foil and continue baking for 15-20 minutes, or until the topping is deeply golden brown, bubbling, and the squash is tender when pierced with a fork.
  14. Let the gratin rest for 10 minutes before serving. This allows the sauce to set properly, preventing a runny result.