This easy sweet potato gratin recipe is made with Gruyère cheese and a cream sauce flavored with garlic and sage. It's similar to a classic potatoes au gratin recipe, but made with sweet potatoes for a fall twist. It's vegetarian and gluten free.
This sweet potato gratin gives you the best of ALL worlds. The perfect combination of sweet, savory, cheesy and creamy.
It makes a perfect side dish for Thanksgiving, Christmas dinner, or any occasion when you want something warm and comforting. Prep is easy and quick, just slice and chop a few things, then let the oven do the work!
If you're like me and you just can't get enough when it comes to gratin recipes, you'll love my Squash Gratin, which you can make with any winter squash. Or maybe you'd like a spicy twist on this recipe? Try my Chipotle Sweet Potato Gratin!
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Sweet potato gratin ingredients
Who knew that you could get this much flavor from so few ingredients? You only need 8 ingredients to make a sweet potato gratin that will knock their socks off!
- Sweet potatoes: Look for sweet potatoes that are heavy for their size. They don't have to all be the same size. You just want to make sure the slices are cut to the same thickness.
- Heavy cream: Heavy cream is key in any gratin or potatoes au gratin recipe. We want a thick, rich sauce, so be sure you're getting the full-fat heavy cream!
- Parmesan cheese: We'll use parmesan cheese to thicken the sauce and to melt on top. Use real parmigiano reggiano and grate it yourself for the best flavor!
- Gruyère cheese: Gruyère is the classic cheese for a gratin. It melts beautifully and has a bit of bold flavor and nuttiness to cut through the cream.
- Garlic, shallots, fresh sage: These aromatics are the key to the amazing flavor in our sweet potato gratin! Garlic and shallots add sweetness, fresh sage adds that amazing fall aroma.
- Unsalted butter: We'll use this to cook down the aromatics.
- Kosher salt: We don't need a lot of salt because the parmesan cheese will add some saltiness.
How to make a sweet potato gratin
Step 1: Peel and slice the sweet potatoes
Preheat the oven to 400 degrees F.
Use a vegetable peeler to peel the sweet potatoes and remove any dark spots. Use a good chef's knife or a mandoline to cut the sweet potatoes into ⅛-inch thick slices.
Transfer the sliced sweet potatoes to a 9x13 baking dish.
Step 2: Grate your cheeses
Grate the parmesan on the small holes of a box grater, then use your fingers to break it down into a finer consistency.
Grate the gruyère on the large holes of the box grater. Set both cheeses aside.
Step 3: Chop and cook the garlic, shallots, and sage
Finely chop the garlic, shallots, and sage.
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Add the butter to a large skillet over medium heat. Transfer the garlic, shallots and sage to the skillet and season with a pinch of salt.
Cook until shallots are soft and translucent, about 5-8 minutes.
Step 4: Make the cream sauce
Reduce the heat to medium low, then add the cream, 2 teaspoons of kosher salt, and 1 cup of the parmesan cheese (about 3 ounces) and stir gently until the cheese is melted.
Bring the mixture almost to a simmer, and cook until it has thickened and reduced slightly. It should be very warm, but not super hot. Don't risk scalding the cream. Taste for seasoning and adjust if necessary.
TIP: The sauce should taste a little bit saltier than you might think. This is the only salt for both the sauce and the sweet potatoes, so it has to carry the weight of seasoning for both.
Step 5: Add the sauce to the sweet potatoes and bake!
Pour the gratin sauce over the sweet potatoes in the baking dish. Cover tightly with foil and bake for about 50 minutes, until the sweet potatoes are fork tender.
Remove the foil and bake for another 10 minutes to allow the sauce to thicken up.
Top with the Gruyère and the remaining parmesan, and return to the oven for another 10 minutes or until the cheese is melted and bubbly.
Allow to stand for 10-15 minutes before serving so the sauce can set up.
Recipe tips
- I always prefer to grate my own cheese with a box grater or food processor. Grated cheese can be a bit dried out, and it usually has an anti-caking agent coating on it that can affect how well it melts.
- Take it easy when heating up the cream mixture. You really want to go low and slow. If you hit it with high heat, you could scorch the cream or cause the sauce to separate and the cheese to clump. And nobody wants that!
- If you don't have fresh sage, you can substitute 2 teaspoons of dried sage, or 1 tablespoon of fresh thyme.
FAQ
Yes, you can! Gruyère is the classic gratin choice, but sweet potatoes also go well with other melting cheeses like fontina, gouda, and cheddar cheese. Or mix up a few different kinds!
You don't need to worry about alternating a layer of sweet potatoes, then a layer of sauce for this gratin. Since all of the cheese is on top, and because our aromatics are all finely diced, the liquid and flavor will find its way into the nooks and crannies of the potatoes all on its own.
Technically you can freeze it, but you will get a very different consistency and texture from the sauce and cheese once reheated. You won't have as much of a creamy texture, but it will still taste good! Allow to thaw in the refrigerator before reheating in the microwave or a 350 degrees F oven.
More sweet potato recipes
- These Savory Roasted Sweet Potatoes have a cilantro-lime sauce and get dotted with yogurt for bright flavors. It's a great Thanksgiving side dish when you want a change from the same old same old.
- Sweet Potato Soup is rich and comforting, made with bacon, sage and coconut milk.
A sweet potato gratin is an easy, cheesy fall side dish!
- You only need a few ingredients.
- Sage gives it all the fall flavor vibes.
- Try it for Thanksgiving instead of potatoes au gratin or sweet potato casserole.
- It's vegetarian and gluten-free!
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Recipe
Sweet Potato Gratin
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Equipment
- mandoline optional
Ingredients
- 3 pounds sweet potatoes
- 1½ cups grated Gruyère cheese
- 1⅓ cups grated parmesan cheese divided (about 4 ounces)
- 1 small shallot
- 3 cloves garlic
- 2 tablespoons finely chopped sage
- 3 tablespoons unsalted butter
- 2 cups heavy cream
- 2 teaspoons kosher salt
Instructions
- Preheat the oven to 400 degrees F. Use a vegetable peeler to peel the sweet potatoes and remove any dark spots. Use a good chef's knife or a mandoline to cut the sweet potatoes into ⅛-inch thick slices. Transfer the sliced sweet potatoes to a 9x13 baking dish.
- Grate the parmesan on the small holes of a box grater, then use your fingers to break it down into a finer consistency. Grate the Gruyère on the large holes of the box grater. Set both cheeses aside.
- Finely chop the garlic, shallots, and sage.
- Add the butter to a large skillet over medium heat. Transfer the garlic, shallots and sage to the skillet and season with a pinch of salt. Cook until shallots are soft and translucent, about 5-8 minutes.
- Reduce the heat to medium low, then add the cream, 2 teaspoons of kosher salt, and 1 cup of the parmesan cheese (about 3 ounces) and stir gently until the cheese is melted. Bring the mixture almost to a simmer, and cook until it has thickened and reduced slightly. It should be very warm, but not super hot. Don't risk scalding the cream.
- Taste the sauce for seasoning and adjust salt if necessary, it should be a LITTLE BIT salty, because it has to season all the sweet potatoes, as well as the sauce.
- Pour the gratin sauce over the sweet potatoes in the baking dish. Cover tightly with foil and bake for about 50 minutes, until the sweet potatoes are fork tender. Remove the foil and bake for another 10 minutes to allow the sauce to thicken up.
- Top with the Gruyère and the remaining parmesan, and return to the oven for another 10 minutes or until the cheese is melted and bubbly. Allow to stand for 10-15 minutes before serving so the sauce can set up.
Notes
-
- I always prefer to grate my own cheese with a box grater or food processor. Grated cheese can be a bit dried out, and it usually has an anti-caking agent coating on it that can affect how well it melts.
-
- Take it easy when heating up the cream mixture. You really want to go low and slow. If you hit it with high heat, you could scorch the cream or cause the sauce to separate and the cheese to clump. And nobody wants that!
-
- If you don't have fresh sage, you can substitute 2 teaspoons of dried sage, or 1 tablespoon of fresh thyme.
Katie Meier
Yum, yum, yum!!! Not a bite of this was left behind at Thanksgiving!
Debra
Hi Katie!
Wow, I'm so glad to hear this was a Thanksgiving hit!
Thanks for reading and trying my recipes!
Debra