- 1 tablespoon butter
- 1 tablespoon olive oil
- 2 large onions, cut into 1-inch squares
- 3 tablespoons chopped fresh sage
- salt and freshly ground black pepper to taste
- 3 pounds butternut squash – peeled, seeded, and cut into 1/2-inch cubes
- 2 cloves garlic, minced
- 3/4 teaspoon salt
- 10 tablespoons heavy whipping cream
- 1 cup fresh bread crumbs
- 1 1/2 tablespoons butter, melted
- Preheat oven to 350 degrees F (175 degrees C). Grease a gratin baking dish with butter.
- Heat 1 tablespoon butter and olive oil in a large skillet over low heat; add onions and sage. Cover and cook, stirring occasionally, until onions are browned, about 25 minutes. Season with salt and black pepper.
- Place a steamer insert into a saucepan and fill with water to just below the bottom of the steamer. Bring water to a boil. Add squash, cover, and steam until tender, 10 to 20 minutes. Transfer squash to prepared gratin dish; toss with garlic and 3/4 teaspoon salt. Add the caramelized onions to the pan and gently mix to combine.
- Warm cream in a saucepan over low heat; pour over squash mixture. Stir to coat. Combine bread crumbs and 1 1/2 tablespoons melted butter together in a bowl; sprinkle over squash mixture.
- Bake in the preheated oven until gratin is bubbling and breadcrumbs are browned, 20 to 25 minutes.