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Butternut Squash Gratin with Caramelized Onions & Gruyere

  • Author: Molly
  • Total Time: 2 hours
  • Yield: 8 servings 1x


This Butternut Squash Gratin with Caramelized Onions & Gruyere is a dish to remember! Tender butternut squash, sweet caramelized onions, sage-infused cream, and nutty gruyere cheese make this one very special. It is the side dish of all side dishes – perfect for the holiday season!



For the Onions:

  • 2 tablespoons butter
  • 8 large sage leaves
  • 2 large yellow onions, thinly sliced
  • 1 tablespoon light brown sugar
  • Pinch of salt

For the Gratin:

  • 1 1/4 cups heavy cream
  • 1/4 cup chopped fresh sage (roughly 2-3 whole sage leaves)
  • 1/2 teaspoon ground nutmeg
  • 1 teaspoon kosher salt
  • 1/2 teaspoon ground black pepper
  • 1 large butternut squash, peeled and cut into thin slices (I used a 3-lb squash)
  • 6 oz grated gruyere cheese
  • 2 oz grated parmesan cheese
  • 1 cup panko breadcrumbs


For the Onions:

  1. Add the butter to a skillet and set over medium heat. Add the sage leaves and cook for a few minutes or until they are crisp. Remove the sage leaves and set aside – we will use these as garnish later.
  2. Add the sliced onions, sugar, and salt and cook, stirring every few minutes, for 25-30 minutes, or until the onions are softened and lightly caramelized. Be patient – this can take some time (and can also be done ahead of time).

For the Gratin:

  1. Preheat the oven to 375°F and grease a large round baking dish (10-12 inches in diameter).
  2. In a measuring cup or bowl, whisk together the cream, sage, nutmeg, salt, and pepper. Pour a couple tablespoons of the cream over the bottom of the greased baking dish.
  3. Add a layer of the butternut squash slices. Add roughly a third of the caramelized onions. Sprinkle over roughly ⅓ of the grated gruyere cheese. Pour over roughly ⅓ of the cream mixture.
  4. Continue layering two more times: squash, onions, cheese, cream.
  5. Sprinkle the grated parmesan cheese and panko breadcrumbs over the top layer. Cover the pan loosely with tin foil and then place the pan on a baking sheet. 
  6. Bake for 50-60 minutes or until a sharp knife goes through the squash easily. Remove the foil and bake for another 10-15 minutes or until the top is golden and the gratin is bubbly around the edges.
  7. Allow to cool for 15 minutes before serving. Just before serving, garnish with the reserved crispy sage leaves.


To make this ahead, I recommend prepping and assembling the gratin in its entirety – except for the breadcrumb topping. Cover and refrigerate the baking dish until you are ready to bake it. Allow it to come to room temperature before baking and add the breadcrumbs just before you put it in the oven.

  • Prep Time: 15 minutes
  • Cook Time: 1 hour 45 minutes
  • Category: side dishes

Keywords: butternut squash gratin, butternut squash and gruyere gratin, butternut squash and caramelized onion gratin, holiday side dishes, thanksgiving side dishes, butternut squash side dishes