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I bake thin, spiral-layered sweet potatoes in garlicky thyme cream with Gruyère and Parmesan, then finish them with crispy fried sage, toasted pecans, and pine nuts. It's a savory, golden sweet potato side dish made for Thanksgiving, Christmas, and cozy fall dinners.
This Spiral Sweet Potato Gratin Is the Prettiest Side on the Holiday Table
Sweet Potato Gratin is a creamy, savory holiday side dish made with thin sweet potato rounds arranged in a spiral, baked in garlic-thyme cream with Gruyère and Parmesan. The edges turn golden and slightly crisp. The center stays soft and creamy. Then the crispy sage and toasted pecans and pine nuts on top add crunch to every bite.
It serves 10 people, so it is perfect for Thanksgiving, Christmas, or any big dinner at home! Think of this as scalloped sweet potatoes, dressed up for the holidays. Here's why it earned a permanent spot on my holiday table:
Why You'll Love It
- Savory, Not Sugary: Garlic, thyme, nutmeg, and two cheeses balance the natural sweetness of the sweet potatoes. If you want a sweet potato side that tastes like dinner instead of dessert, this is it.
- The Spiral Look: Standing the rounds on their edges gives you golden, crispy tips on top and tender, creamy layers underneath. It looks impressive, but it's just slicing and stacking.
- Gruyère and Parmesan Cream: Gruyère adds a nutty, melty richness. Parmesan adds a salty bite. Together they make the sauce taste much more complex than the short ingredient list suggests.
- Don't Get Me Started on the Topping: Toasted pecans, toasted pine nuts, and sage leaves fried in butter. A drizzle of the sage butter at the end takes it over the top.
- Holiday-Friendly Timing: The gratin bakes mostly hands-off. I toast the nuts and fry the sage while it finishes in the oven, so everything is ready at the same time.
- For more holiday sides, try my hasselback butternut squash with candied pecans, green beans with pine nuts, Brussels sprouts with bacon, pecans, and cranberries, creamy mashed potatoes with roasted garlic, and sausage-stuffed acorn squash. Planning the whole menu? Browse my list of 60 Thanksgiving side dishes.
Ingredients and Substitutions
This recipe has 2 components: sweet potato gratin and a crunchy nut and crispy sage topping. Read on for helpful tips, or scroll down to the recipe card for the ingredient amounts and complete instructions.
1) Sweet Potato Gratin Ingredients
- Sweet potatoes: Look for long, relatively straight sweet potatoes with a similar diameter along their length. These give you more evenly sized rounds and make the spiral much easier to arrange. Very large or irregularly shaped sweet potatoes can be more difficult to work with. I recommend orange-fleshed sweet potatoes. They become tender and creamy when baked and have a lovely natural sweetness that balances the savory cheese sauce.
- Heavy cream: Heavy cream gives this gratin its rich texture and helps balance the natural sweetness of the potatoes. It also holds up better during baking than a mixture with a larger amount of milk.
- Gruyère cheese: Grate it yourself, since pre-shredded cheese has anti-caking agents. Swiss, Fontina, or white cheddar are good substitutes.
- Parmesan cheese: Freshly grated for the best flavor. Pecorino Romano also works.
- Unsalted butter: Softened, for greasing the baking dish.
- Garlic: Finely grated, so it melts into the cream.
- Fresh thyme: You can use 1 teaspoon of dried thyme if needed, but fresh tastes brighter.
- Ground nutmeg: Just a little. It's a classic flavor in a gratin.
- Kosher salt and black pepper: Sweet potatoes need good seasoning to balance their sweetness.
2) Topping Ingredients
- Pecans: Roughly chopped. Walnuts or hazelnuts are a good swap.
- Pine nuts: You can leave them out and add more pecans instead.
- Unsalted butter: For frying the sage. Save this butter, because it tastes amazing drizzled over the gratin.
- Fresh sage leaves: They turn crisp in about 30 seconds. Don't use dried sage here.
- Fresh thyme sprigs: For garnish.
How to Make Sweet Potato Gratin (Step-by-Step Photos & Tips)
This is a recipe overview. Scroll down for complete instructions + ingredient amounts in the recipe card above.
- Preheat & prep. Preheat the oven to 350°F (175°C). Grease an 11-inch round baking dish or braiser with soft butter.
- Slice the sweet potatoes. Peel the potatoes and slice them into ⅛-inch rounds with a mandoline. Keep the slices in small stacks so they're easy to grab.
- Arrange the spiral. Start at the outer edge and lean the slices against each other in tight, overlapping rows. Work toward the center and tuck small slices into any gaps.
- Warm the cream. Heat the cream with garlic, thyme, nutmeg, salt, and pepper over low heat for 3-5 minutes. Keep it below a boil. Take it off the heat and let it cool slightly.
- Stir in the cheese. Add the Gruyère and Parmesan and stir slowly. It's fine if the cheese doesn't fully melt.
- Pour the sauce. Pour the cream slowly between the slices, stirring as you go. Stop once the potatoes are mostly covered so the spiral still shows.
- Bake covered, then uncovered. Bake covered for 45-50 minutes, then check with a knife. Uncover and bake 25-35 minutes more until tender and golden at the edges. (Need more color? Bump the oven to 375°F (190°C) for the last 5-10 minutes.)
- Toast the nuts. Toast the pecans in a dry skillet for 3-5 minutes, then the pine nuts for 2-3 minutes. Keep them on separate plates.
- Fry the sage. Melt butter until foamy, add the sage, and fry 20-40 seconds until crisp. Save the sage butter!
- Rest & top. Let the gratin rest 15 minutes. Scatter the nuts, crispy sage, and fresh thyme over the top. Drizzle with sage butter and serve warm.
Tips for Slicing Potatoes and Arranging the Spiral
- Slice evenly: I use a mandoline (with the safety guard or a cut-resistant glove) to cut slices about ⅛ inch (3 mm) thick. Thicker slices cook slowly and won't fan out, and very thin ones turn mushy. Don't rinse the slices, because their starch helps thicken the sauce.
- It doesn't need to be perfect. The important thing is to keep the slices closely overlapping and angled slightly so they support one another.
- Start at the outside edge and work inward, following a gentle curve. Save the smaller slices to fill the center.
- Keep the slices at a fairly even height so the exposed edges brown evenly.
What to Serve with Sweet Potato Gratin
It's a natural with roast turkey or honey brown sugar glazed ham, but I also love it with:
Sweet Potato Gratin with Gruyère and Parmesan
I bake thin spiral-layered sweet potatoes in garlicky thyme cream with Gruyère and Parmesan until tender, creamy, and golden. Then I top it with toasted pecans, pine nuts, and crispy fried sage. This savory sweet potato gratin is a showstopping Thanksgiving and holiday side dish.
Ingredients
Sweet Potato Gratin
- 1 tablespoon unsalted butter softened, for greasing
- 3 pounds sweet potatoes orange-fleshed, peeled
- 1 ⅔ cups heavy cream
- 4 cloves garlic finely grated
- 1 tablespoon fresh thyme leaves
- ¼ teaspoon ground nutmeg
- 1 ½ teaspoons kosher salt
- ½ teaspoon black pepper freshly ground
- 1 cup Gruyère cheese freshly grated
- ⅓ cup Parmesan cheese freshly grated
Topping
- ⅓ cup pecans roughly chopped
- 3 tablespoons pine nuts
- 2 tablespoons unsalted butter
- 15 fresh sage leaves
- Fresh thyme sprigs for garnish
Instructions
- Preheat the oven to 350°F (175°C). Lightly grease an 11-inch round ovenproof baking dish or braiser with the softened butter.
- Slice the sweet potatoes: Using a mandoline, slice the peeled sweet potatoes into even ⅛-inch-thick rounds. Try to keep the slices together in small stacks as you work. This makes them easier to arrange.
- Arrange the spiral: Starting around the outside edge of the prepared baking dish, arrange the sweet potato slices in tightly overlapping rows, leaning them slightly against one another. Continue working toward the center to create a spiral pattern. Use smaller slices to fill any gaps in the middle.
- Make the cream sauce: Add the heavy cream, garlic, thyme, nutmeg, salt, and black pepper to a small saucepan. Warm over low heat for 3-5 minutes, stirring occasionally, until fragrant. Do not allow the cream to boil. Remove from the heat and let cool slightly.
- Add the grated Gruyère and Parmesan to the warm cream and stir slowly until evenly distributed. The cheese does not need to melt completely. Do not return the saucepan to the heat.
- Slowly pour the cream mixture over and between the arranged sweet potatoes. Stir the mixture occasionally as you pour to keep the cheese evenly distributed. Depending on the depth of your dish and how tightly the potatoes are packed, you may not need all of the sauce. Aim to cover the potatoes without drowning them, so the spiral is still visible once the dish is cooked.
- Bake covered: Cover the baking dish with a lid or aluminum foil and bake for 45-50 minutes, until the sweet potatoes are beginning to soften. Carefully remove the cover and check the potatoes with the tip of a sharp knife. If they are still very firm, cover and bake for another 10-15 minutes.
- Bake uncovered: Remove the lid or foil and continue baking uncovered for 25-35 minutes, until the sweet potatoes are completely tender, the sauce has thickened, and the exposed edges are lightly golden. If the potatoes are tender but need more color, increase the oven temperature to 375°F (190°C) for the final 5-10 minutes, watching carefully to prevent burning.
- Toast the nuts: While the gratin finishes baking, place the chopped pecans in a dry skillet over medium-low heat. Toast for 3-5 minutes, stirring frequently, until fragrant. Transfer to a plate. Add the pine nuts to the skillet and toast for 2-3 minutes, stirring frequently, until lightly golden. Transfer to a separate plate, then wipe out the skillet.
- Fry the sage: Add the 2 tablespoons of butter to the skillet over medium heat. Once the butter begins to foam, add the sage leaves. Fry for 20-40 seconds, until crisp, then transfer to a paper towel-lined plate. Reserve the fragrant butter.
- Rest and serve: Remove the gratin from the oven and let it rest for 15 minutes. Scatter the toasted pecans, pine nuts, and crispy sage leaves over the top, then garnish with fresh thyme. Drizzle with a little reserved sage butter, if desired, and serve warm.
Notes
- Baking Dish: I use an 11-inch (28 cm) round baking dish or braiser. Any similar ovenproof dish works if it's deep enough to hold the cream. A smaller dish needs less sauce, and baking time can change, so always check for tenderness.
- Alternative Baking Dish: A 9x13-inch dish works too. Arrange the slices in straight overlapping rows and start checking for tenderness a little earlier.
- Use a mandoline for even slices: Even ⅛-inch rounds cook at the same rate. Use the hand guard, since sweet potatoes are firm and can slip.
- Cheese: Grate the Gruyère and Parmesan from a block. Pre-shredded cheese doesn't melt as smoothly into the cream.
- Warm, don't boil, the cream: Gently warm it with the garlic, thyme and seasonings before pouring it over the potatoes. Boiling cream can separate once the cheese goes in. Low and slow is all you need.
- Don't drown the potatoes: The full amount of sauce is right for an 11-inch (28 cm) round dish. Too much sauce bubbles over the spiral and hides it, so you may have some left over with a smaller or tightly packed dish.
- Bake until tender: Plan on 1 hour 15 minutes to 1 hour 30 minutes. It's done when a knife slides through the potatoes easily, the sauce is gently bubbling and thick, and the edges are lightly browned.
- Potatoes tender but tops still pale? Raise the oven temperature slightly for the last few minutes.
- Edges browning too fast but potatoes still firm? Loosely cover the dish and keep baking until tender.
- Make the toppings: Toast the nuts over medium-low heat, stirring often so they don't burn, then let them cool. Fry dry sage leaves briefly in butter and remove them as soon as they crisp. You can drizzle a little of the sage butter over the gratin.
- Let it rest: Rest the gratin for at least 15 minutes so the sauce settles and the spiral shows. This gives the bubbling cream time to settle and thicken slightly, so the potatoes are easier to serve. Resting also helps the spiral show if the sauce rose around the potatoes during baking.
- Add the nuts, sage, and thyme right before serving. This keeps them crunchy and stops them from burning in the oven.
- Special Tools: 11-inch Round Braiser or Baking Dish | Mandoline | Small Saucepan | Skillet | Sharp Knife | Aluminum Foil | Microplane Grater
Make Ahead
- Bake it a day ahead: Bake the gratin, let it cool and refrigerate it without the toppings.
- Reheat: Cover and reheat at 325°F (165°C) until heated through, then uncover briefly to refresh the top.
- Toppings: Make the toasted nuts and crispy sage separately and add them just before serving.
- For the prettiest look, I recommend baking the gratin fresh on the day you serve it.
Storage and Reheating
- Refrigerator: Cool the gratin, then move leftovers to an airtight container or cover the dish tightly. Refrigerate within 2 hours of cooking and store for up to 3 to 4 days. Store leftover nuts and crispy sage separately so they don't get soft.
- Reheating in the oven: Preheat the oven to 325°F (165°C). Place the gratin in an ovenproof dish, cover loosely with foil and reheat for about 15 to 25 minutes, until heated through (165°F / 74°C in the center). Larger portions need extra time. Remove the foil for the last few minutes to refresh the golden edges.
- Reheating in the microwave: This works for single portions, though the potatoes will lose some of their crisp edges.
- Freezer: I don't recommend freezing. Cream-based sauces can separate when thawed, and the sweet potatoes may turn softer and release extra liquid.
Nutrition
Nutrition Information
Sweet Potato Gratin with Gruyère and Parmesan
Amount per Serving
Calories
396
% Daily Value*
Fat
27
g
42
%
Saturated Fat
15
g
94
%
Trans Fat
0.1
g
Polyunsaturated Fat
3
g
Monounsaturated Fat
8
g
Cholesterol
71
mg
24
%
Sodium
583
mg
25
%
Potassium
553
mg
16
%
Carbohydrates
30
g
10
%
Fiber
5
g
21
%
Sugar
7
g
8
%
Protein
9
g
18
%
Vitamin A
20181
IU
404
%
Vitamin C
5
mg
6
%
Calcium
250
mg
25
%
Iron
1
mg
6
%
* Percent Daily Values are based on a 2000 calorie diet.
Nutrition Disclaimer:
The nutritional information on this website is only an estimate and is provided for convenience and as a courtesy only. The accuracy of the nutritional information for any recipe on this site is not guaranteed. It should not be used as a substitute for a professional nutritionist's advice.
Frequently Asked Questions
- Can I make sweet potato gratin ahead of time? Yes. Bake it completely up to 1 day ahead, cool, cover, and refrigerate. Reheat covered at 350°F (175°C) for 25 to 30 minutes. Make the nut and sage topping fresh so it stays crunchy.
- Do I need a mandoline? No, but it helps. A sharp chef's knife works too. Just aim for even slices so everything cooks at the same rate.
- Can I use a 9x13-inch pan? Yes. Arrange the slices in straight overlapping rows instead of a spiral. Start checking for tenderness a little earlier, since the layer will be shallower.
- Why is my gratin watery? It usually needs more time uncovered, or it was cut too soon. The 15-minute rest gives the cream time to thicken.
- Do I bake this covered or uncovered? Both. Covered first so the potatoes steam and soften, then uncovered so the top turns golden.
- Can I skip the nuts? Absolutely. The crispy sage and thyme alone make a lovely garnish.
More Favorite Holiday Side Dishes
- Roasted Fall Vegetables (Maple-Cinnamon Butternut Squash and Brussels Sprouts)
- Hasselback Butternut Squash with Sage-Honey Butter and Candied Pecans
- Easy Scalloped Potatoes with Parmesan, Garlic, and Thyme
- Mashed Potatoes with Roasted Garlic and Parmesan
- Apple Stuffed Acorn Squash with Cinnamon and Brown Sugar
- Sweet Potatoes and Broccoli with Pecans and Cranberries
- Creamy Roasted Butternut Squash Soup
- Garlic Butter Dinner Rolls
- 60 Thanksgiving Side Dishes That Will Outshine the Turkey
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