I made this butternut squash gratin for the first time for Canadian Thanksgiving and everyone went crazy for it. Using butternut squash instead of potatoes makes it lighter and more flavorful than a traditional potato gratin, plus the thin slices bake up tender in a creamy Gruyère and sage sauce under a golden breadcrumb top. The thing that sets this one apart is the sauce: I simmer the onions, garlic and sage with chicken broth and cream until it starts to thicken, then melt in half of the Gruyère before it ever goes into the dish, which prevents the gratin from being too liquidy after baking.
It’s a holiday side dish that looks far more impressive than the effort it takes, and since you can assemble it up to 3 days in advance and just bake it before serving, it’s one less thing to do on the big day. If you’re planning a full Thanksgiving spread, my Brussels Sprout, Bacon & Kale Gratin is dairy free, so it’s a great one to have on the table for anyone who can’t have cream, and my Scalloped Potatoes with Caramelized Fennel & Onions are there for the potato lovers who want the classic.
Key Ingredients You Will Need
Butternut squash: I slice the squash about 1/8 inch thick so the layers bake up tender in the same time it takes the top to turn golden. I’m far too klutzy to use a mandoline, so I simply cut it by hand, but feel free to use one if you prefer. I like to start with the neck of the squash, since it’s solid all the way through and gives you neat half-moon slices, then move on to the rounder base, where the seeds leave a hollow in the middle of each slice.
Heavy cream: I prefer using heavy cream because its higher fat content means it’s much less likely to curdle as it simmers, plus it thickens into a rich, silky sauce that clings to every layer of squash. Half and half also works if you’d like a lighter gratin, just keep it at a gentle simmer rather than a boil so it doesn’t separate, and give it a few extra minutes to thicken.
Gruyère: I melt half of the Gruyère right into the sauce and sprinkle the rest between the layers, so you get that rich, cheesy flavor in every bite rather than just on top.
How To Make Butternut Squash Gratin
1. Soften the onions and sage. Give the onions a few minutes on their own before adding the sage, then keep cooking until they’re soft and translucent like this. Softened onions melt into the sauce rather than staying crunchy between the layers.
2. Thicken the sauce. This is the step that keeps the gratin from being soupy. Once the broth and cream have simmered for about 5 minutes, the sauce should coat the back of a spoon like this, then take it off the heat and stir in half of the Gruyère until it melts.
3. Layer the squash and sauce. Overlap the slices slightly and pack them in tightly so there aren’t any big gaps, then spoon about a third of the sauce over each layer with a light sprinkle of Gruyère. I save the neatest slices for the top layer so it looks its best once it comes out of the oven.
4. Top and bake. Spread the last of the sauce over the top and scatter over the breadcrumbs. The foil lets the squash steam until tender, then a minute or two under the broiler turns the top golden.
Tips For Making the Best Butternut Squash Gratin
- Slice the squash as evenly as you can. Whether you cut it by hand like me or use a mandoline, keeping the slices close to 1/8 inch means they all turn tender at the same time, without some pieces still firm in the middle.
- Watch it closely under the broiler. The breadcrumbs go from golden to burnt in a matter of seconds, so I stay right by the oven for that last minute or two.
- Let it rest before serving. A few minutes out of the oven gives the sauce time to settle, so it’s much easier to scoop out neat portions.
Ways To Customize
Sweet Potato: You can swap the butternut squash for sweet potatoes, just slice them to the same 1/8 inch thickness so they cook through evenly.
Vegetarian: Use vegetable broth in place of the chicken broth.
Gluten Free: Use gluten-free breadcrumbs, and check the label on your broth.
How To Store & Reheat
Make Ahead: You can assemble this butternut squash gratin up to 3 days in advance. Cover it tightly and keep it in the fridge, then bake it straight from the fridge right before serving.
Storage: Store leftovers in an airtight container in the fridge for up to 4 days.
Reheating: Warm leftovers covered with foil in a 350°F oven until heated through, or in the microwave in short bursts.
If you make this Butternut Squash Gratin, let me know in the comments section below. I would love to hear what you think or take a photo and tag me (@everylastbite) on Instagram. I love seeing your photos!
Butternut Squash Gratin
Ingredients
- 2 lbs butternut squash halved, peeled and sliced 1/8 inch thick
- 1 tbsp butter
- 1 large yellow onion thinly sliced
- 3 cloves garlic minced
- 1/2 tsp salt
- 5 sage leaves thinly sliced
- 1/2 cup chicken broth
- 1 cup heavy cream
- 1/8 tsp nutmeg
- 1/4 tsp pepper
- 1 cup grated Gruyère cheese divided
- 1/4 cup breadcrumbs
Instructions
- Preheat the oven to 400°F and lightly grease an 11×7 inch baking dish.
- In a skillet on medium-high heat, melt the butter, then add the thinly sliced onion and garlic. Season with salt and sauté for 3 minutes, then add the sage and sauté for an additional 4-5 minutes until the onion has softened.
- Pour in the chicken broth and bring to a gentle simmer, then pour in the heavy cream. Stir in the nutmeg and pepper and leave to gently simmer for 5 minutes until the sauce begins to thicken. Remove from the heat and stir in 1/2 cup of the grated Gruyère until it melts into the sauce.
- Add a thin layer of butternut squash slices to the greased baking dish so they overlap slightly. Pour 1/3 of the sauce over the squash and sprinkle with half of the remaining Gruyère, then add another thin layer of squash, followed by another 1/3 of the sauce, the rest of the Gruyère and a final layer of squash. When layering, make sure everything is packed tightly together without big gaps. Top with the last of the sauce, then sprinkle the breadcrumbs over the top.
- Cover the baking dish with foil and bake for 40 minutes. Remove the foil, turn the oven to broil and cook for an additional 1-2 minutes until the breadcrumbs are golden brown, watching carefully so they don’t burn.
- Remove from the oven and let the gratin rest for a few minutes before serving.
Notes
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