Fall has a habit of sneaking up on me. The quality of sunlight pales into a lovely shade of translucent yellow. The air crisps up; perhaps there is a whiff of fire smoke. And before we know it, we’re all cozied up in scarves and hats and thick socks, pulling musty coats from their summer homes beneath beds and in the backs of closets, and fantasizing about soups and rich mugs of hot chocolate.
This gratin, however, does no sneaking. It’s straightforward in its enthusiasm for the season, but graciously so. It employs a host of cozy flavors that give great depth to the dish; the butternut squash is bathed in apple cider vinegar, tossed with caramelized onions and topped with nutty Gruyere cheese, fresh sage and crunchy, toasted hazelnuts.
Butternut Squash Gratin
3 pounds butternut squash, peeled
3 tablespoons apple cider vinegar
3 tablespoons olive oil, divided
1 medium yellow onion, sliced lengthwise
1.5 cups shredded Gruyere cheese
1/3 cup toasted hazelnuts, chopped
2 tablespoons fresh, chopped sage
Sea salt and freshly ground black pepper
Preheat oven to 400 degrees.
Slice the butternut squash into 1/2″ rounds, then quarter each round. Remove seeds. Toss the diced squash in the apple cider vinegar and two tablespoons of olive oil. Arrange on a large baking sheet and generously salt and pepper.
Roast squash until cooked through but still firm, about 30-35 minutes.
While the squash is roasting, caramelize the onions. Place in a medium skillet over a low flame. Cover, stirring occasionally, until the onions are soft and jammy, about 20-25 minutes.
Remove squash from oven and set aside to cool, about ten minutes.
Grease a medium cast-iron skillet or casserole dish. Arrange a layer of squash, followed by a layer of onions. Add the remaining squash. Sprinkle the Gruyere cheese evenly over the squash, followed by the toasted hazelnuts and one tablespoon of the sage.
Bake the gratin until the cheese is golden and melted, about another 20 or 30 minutes.
Remove from the oven, and top with the remaining sage.