This vegetarian butternut squash gratin recipe is a healthy version made without cream or breadcrumbs that’s still incredibly delicious. Scalloped squash pieces are layered with gruyere and parmesan cheeses, a lightly sweetened walnut crumble, and a garlic thyme olive oil sauce. If you need a butternut squash side dish for Thanksgiving to WOW your loved ones and make ahead of time, this elegant casserole for you!
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Lizzie’s Notes
There’s nothing quite like layering and baking a gratin to get me in the mood for the holiday season! There’s something therapeutic about arranging thinly sliced vegetables in a pan, and the finished casserole is always so beautiful. Plus, who doesn’t love something covered with melted cheese?
This butternut squash gratin became an instant favorite the moment I tasted a creamy, savory, nutty bite. It’s got plenty of the quintessential holiday fare ingredients, like squash, cheese, nuts, and even a little brown sugar, but it’s much lighter than scalloped potatoes or casseroles that go a little too hard on the cream and cheese.
I think this recipe would be a lovely addition to your Thanksgiving table (and a conversation starter!), but don’t be afraid to give it a go for dinner one night. It will make any meal feel special!
Ingredients and Substitutions
- Butternut squash: Sub delicata or honeynut squash if that’s what you have.
- Extra virgin olive oil: Some of my favorite brands are Partanna and Zoe. I recommend high-quality olive oils because they are a significant ingredient in this butternut squash gratin. You want something that tastes good!
- Butter: I add a little butter to the sauce, but you can substitute more olive oil if that’s what you prefer.
- Shallots: Use red or yellow onion or even leeks if you don’t have shallots.
- Garlic: Freshly pressed or minced garlic cloves taste best in this recipe, but you can substitute about a teaspoon of garlic powder if that’s what you have on hand.
- Vegetable broth: Sub chicken broth if needed.
- Thyme: Use dried thyme (about 2 teaspoons) if you don’t have fresh. Rosemary or parsley would also work.
- Parmesan and gruyere cheeses: I prefer to buy blocks that I then grate myself with a hand or box grater. You can use pre-shredded if you want. If you need the recipe to be strictly vegetarian, look for cheeses labeled as such.
- Walnuts: Sub pecans if desired.
- Brown sugar: Use light or dark. I don’t recommend substituting a liquid sweetener because of the long baking time.
- Nutmeg: Sub cinnamon if you don’t have nutmeg.
Instructions
The full recipe card and ingredients list for butternut squash gratin is at the bottom of the post. Here’s a preview of the steps with photos to guide you in the kitchen.
Cook garlic and shallots in olive oil until lightly browned.
Add the rest of the olive oil, butter, thyme, and broth. Cook until the butter is melted. Remove from heat and reserve.
Peel and trim the squash. Slice it in half where the top ends and base begins. Slice the base in half and scoop out the seeds. Use a mandoline or sharp knife to make THIN disks.
Grease a 12-inch cast iron skillet or oval baking dish. Add a small amount of broth, then make a layer of squash slices overlapping like shingles.
Drizzle a third of the olive oil sauce over the first layer of squash. Sprinkle a third of the chopped walnuts mixed with brown sugar a nutmeg.
Add a third of each of the shredded parmesan and gruyere cheeses.
Repeat two more times to have a total of three layers.
Cover tightly with foil. Bake for 35 to 45 minutes at 400 degrees F/204 degrees C until the squash is tender. Uncover and bake for 5 to 10 more minutes.
Equipment
For best results, use a mandoline to slice the squash. I use the mandoline blade of the Oxo Complete Grate and Slice Set when I want really thin slices of vegetables.
To bake butternut squash gratin, use an oven-safe dish such as a 12-inch cast iron skillet or 11- to 12-inch oval baking dish. A 9×13 inch casserole pan also works if you don’t have a round or oval dish. Please note: the onion and squash will caramelize during the baking process and some pieces may turn a dark brown color. This is most pronounced if you use a cast iron pan, likely due to the reaction between the onion and garlic in the sauce and the pan. While the dark pieces are harmless and safe to eat, use a dish other than a cast iron if you care about what color they are.
Make Ahead, Storage, and Reheating
To make butternut squash gratin in advance, layer and prepare the dish following all of the steps up until putting it in the oven. Cover tightly with foil and place in the fridge for up to 12 hours. Bake when you are ready to eat it.
You can also bake the gratin in advance and keep it covered in the fridge for up to 6 hours. Reheat it in the oven, covered with foil, at 350 degrees F/177 degrees C for 10 to 15 minutes until warmed through. This method is helpful if you are bringing the dish to someone else’s home for a holiday dinner.
Leftovers will last in an airtight container in the refrigerator for 2 to 3 days. Reheat in the microwave in 30-second intervals on high until warmed through.
More Squash Recipes
If you love this butternut squash gratin, check out the following winter squash recipes while you’re here. You may also enjoy the Turnip and Beet Gratin with Gruyere and Mushroom Gratin.
📖 Recipe
Butternut Squash Gratin
Equipment
- 12-inch cast iron skillet or round or oval baking dish (see notes)
Ingredients
- 1.5 pounds butternut squash - about 1 small squash
- 6 tablespoons extra virgin olive oil - divided
- 2 large shallots - diced, about 1 cup
- 4 cloves garlic - minced
- 2 tablespoons fresh thyme leaves
- 2 tablespoons salted butter
- ¾ cup vegetable broth - divided
- ½ teaspoon freshly ground black pepper
- ¼ teaspoon salt
- 1 cup roughly chopped walnuts
- 2 tablespoons light brown sugar
- ½ teaspoon ground nutmeg
- 3 ounces gruyere cheese - freshly grated, about 1 and ¼ cup
- 2 ounces parmesan cheese - freshly grated, about ¾ cup
Instructions
- Preheat the oven to 400℉/207℃. Grease a 12-inch cast iron skillet or 11- to 12-inch oval or round baking dish with butter and set aside.
- Peel and trim the butternut squash. Slice the squash in half where the top meets the base. Cut the base in half lengthwise and scoop out the seeds. Use a mandoline or very sharp knife to slice the squash pieces into thin disks. If you are using a knife, make sure the disks are ⅛-inch thick or thinner.The slices from the top portion of the squash will be perfect circles, but the slices from the halved base will be half-circles. You can tuck the half-circles into the bottom layers of the gratin and use the full circles where they'll be visible on top if desired.
- Prepare the gratin sauce. Warm 2 tablespoons of the olive oil in a medium skillet over medium heat. Add the diced shallots and cook for a few minutes until lightly browned. Add the garlic and cook for a minute until fragrant. Stir in the rest of the olive oil, thyme, butter, ½ cup of vegetable broth, pepper, and salt. Cook until the butter is melted. Remove from heat.
- In a small bowl, stir together the chopped walnuts, brown sugar, and nutmeg. Prepare the grated cheeses.
- Layer the gratin. First, pour the the remaining ¼ cup of broth into the bottom of the greased pan. Next, make a layer of butternut squash slices by overlapping them like shingles. Drizzle about ⅓ of the olive oil sauce over the first layer of squash. Sprinkle ⅓ of the walnut brown sugar mixture on top, followed by ⅓ of each the gruyere and parmesan cheeses.
- Repeat the process two times, each with another layer of squash, ⅓ of the olive oil sauce, ⅓ of the walnut brown sugar mixture, and ⅓ of the cheeses.
- Cover the pan tightly with aluminum foil. Place it on the center rack of the preheated oven. Cook for 35 to 45 minutes until the squash is tender and browned around the edges and the cheese is melted. Remove the foil and bake for another 5 to 10 minutes until browned to your liking (if you want it more browned; this step is optional). Be careful not to cook it for too long with the foil removed so that the walnuts don't burn.
- Scoop onto dishes and enjoy!
- Leave a rating or review by tapping the stars on this recipe card (above) or in the comments section (at the end of the post)!
Notes
- Equipment note: This dish looks beautiful in a round or oval dish, like a cast iron skillet or oval casserole dish. If you choose to use a cast iron, please note that the bottom layer and edges of the gratin will turn a dark brown color as they caramelize in the oven, partially due to the reaction of the shallot and garlic sauce with the iron pan. This is harmless and fine to eat, but if you don’t want the dark brown color on the bottom, you can bake the gratin in a dish that isn’t cast iron.
- Make ahead: You can layer the gratin and bake it at a later time by following the steps up until putting it in the oven. Cover tightly with foil and keep in the refrigerator for up to 12 hours, then bake when you are ready. Alternatively, you can bake the dish and reheat it at a later time. Keep it covered with foil in the refrigerator for up to 6 hours, then reheat covered in the oven for 10 to 15 minutes at 350 degrees F/176 degrees C. Keep a close eye on it so the walnuts don’t overcook/burn.
- Leftovers: Store leftovers in an airtight container in the refrigerator for 2 to 3 days. Reheat in the microwave in 30-second intervals on high until warmed through.
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