Butternut Squash Gratin

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.