Butternut Squash Gratin with Onion and Sage

Assemble two gratins, but don't top with the breadcrumbs. Store in the refrigerator overnight.

Serves 4 to 6 as a side dish

1 tablespoon unsalted butter; more for the gratin dish
1 tablespoon olive oil
2 large onions, chopped into 1 inch squares (about 4 cups)
3 tablespoons chopped fresh sage
3 pounds butternut squash, peeled and cut into 1/2 inch cups (about 8 cups)
2 cloves minced garlic
kosher salt
freshly ground pepper
1/2 cup plus two Tablespoons heavy cream, heated until warm
1 cup fresh breadcrumbs
1 1/2 tablespoons melted unsalted butter

Heat the oven to 350 degrees. lightly coat dish in butter.

In a large skillet, over low heat, melt butter with oil, Add onions and sage. Cover and cook over the heat while you fix the squash.

Put the squash in a steaming basket and set over simmering water. Cover and let steam until the squash is tender, about ten minutes. Put the squash in the prepared dish with the garlic and 3/4 teaspoon salt. Toss gently to combine.

Continue to cook the onions, stirring frequently until they caramelize, about 25 minutes total. Season with salt and pepper and add them to the gratin dish, mixing them with the squash. Pour the warm cream over the vegetables.

Toss the breadcrumbs with the melted butter and sprinkle the crumbs evenly over the gratin. Bake until the top is browned and bubbling, about 40 minutes.