Sweet Potato Gratin with Gruyere Cheese
Sweet potato gratin with Gruyere cheese is a comforting baked casserole of thinly sliced sweet potatoes layered in a sage-infused cream, topped with nutty Gruyere, and baked until the sweet potatoes are tender and the cheese turns golden. It is creamy, savory, and a little bit sweet, and it comes together with just a handful of simple ingredients. If you want one dish that turns a weeknight dinner into something that feels special, this is it.
The term “au gratin” refers to covering a food with cheese, breadcrumbs, or another topping and baking it until the top layer becomes golden and crispy. Here, the sweet potatoes slowly soften in warm cream while they bake covered, then a blanket of Gruyere is added at the end so it melts and browns into that irresistible top layer.
Why I keep coming back to the gratin method
Baking vegetables au gratin is one of the oven cooking methods I choose quite frequently, especially when cooking cauliflower, broccoli, or green beans. Of course, I also like it with potatoes, and recently I discovered that it enhances the sweet aroma of sweet potatoes, especially in combination with a special cheese. If you love this style of cooking as much as I do, take a look at my other gratin recipes, such as this Spinach and Cauliflower Gratin or this Lentils and Veggies Gratin.
For this recipe I chose to use Gruyere cheese, a semi-hard cheese originating in Switzerland, which has a complex and deep taste with notes of nuts and dried fruits. That richness is what balances the natural sweetness of the potatoes so beautifully, and it is why this pairing works so well.
The ingredients you’ll need
This is a short ingredient list, and each item earns its place. Here is what goes into the dish and why it matters:
- Sweet potatoes (4, peeled) – the heart of the dish. Slice them thin and even so they cook through and layer neatly.
- Liquid cream (2 cups) – this is the cooking liquid that turns everything silky. It gently poaches the sweet potatoes as they bake.
- Gruyere cheese (1 cup, grated) – the nutty, deep-flavored topping that browns beautifully. If you cannot find Gruyere, Comte or Emmental are close Alpine cousins.
- Fresh sage (5 to 10 leaves) – infused into the warm cream, sage adds a savory, earthy note that plays against the sweetness.
- Butter (1 tablespoon) – for greasing the dish so nothing sticks.
- Salt and pepper (1 teaspoon each) – to season the cream.
How to get it right, step by step
The full measurements and timings are in the recipe card below, but a few small details make the difference between a good gratin and a great one:
- Slice thin and even. A vegetable mandoline gives you uniform slices that cook at the same rate. Arrange them overlapping in the dish, like a ratatouille, so every layer soaks up the cream.
- Infuse the cream off the heat. Warm the cream until bubbles appear and it just begins to boil, then take it off the heat, season it, add the sage, cover, and let it steep for 5 to 10 minutes. That resting time is where the flavor develops.
- Bake covered first. Cover the casserole with a lid or foil for the first 40 minutes so the sweet potatoes steam and soften all the way through without the top drying out.
- Add the cheese at the end. Sprinkle on the Gruyere only for the last 10 minutes, baking uncovered until it melts and turns golden brown.
- Let it rest before serving. Give the gratin a few minutes to cool and set. This makes it easier to slice and lets the cream thicken around the potatoes.
What to serve with sweet potato gratin
This gratin is rich enough to be the star of the plate, so I like to pair it with something fresh and light, like a crisp green salad or roasted greens. It also makes a lovely holiday side next to a hearty main. If you are cooking a full sweet potato feast, you might enjoy my Garlicky Smashed Sweet Potatoes or these cozy Stuffed Sweet Potatoes, and you can browse even more ideas in my collection of sweet potato recipes.
Make ahead and storing leftovers
You can assemble the gratin a few hours ahead and keep it covered in the fridge, then bake it when you are ready. Leftovers keep well in an airtight container in the refrigerator for up to three days. Reheat individual portions in the oven or a covered dish so the cream loosens again and the top crisps back up. If you would rather make a plant-based version another time, my Vegan Scalloped Potatoes use a similar layered technique without any dairy.
I hope you’ll love this recipe as much as I do. If it earns a spot on your table, please come back to leave a star rating and a comment below, and tell me whether you kept it classic with sage or gave it a twist of your own.
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Sweet Potato Gratin with Gruyere Cheese
Ingredients
- 1 tablespoon of butter
- 4 sweet potatoes peeled
- 2 cups of liquid cream
- 5-10 sage leaves
- 1 teaspoon salt
- 1 teaspoon pepper
- 1 cup grated Gruyere cheese
Instructions
- Heat the oven to 180 C (365F).
- Grease the gratin casserole with butter.
- Cut the peeled potatoes into slices using a vegetable mandoline.
- Put the potato slices in the casserole, arrange them like a ratatouille.
- Pour the cream into a small saucepan and heat it over low heat, until bubbles appear on the surface, and the cream begins to boil. Remove the saucepan from the heat, add salt and pepper, add 5 sage leaves, cover and let the cream infuse for 5-10 minutes.
- Pour the cream mixture over the potatoes in the casserole. Cover the casserole with a lid or foil.
- Put the casserole in the oven for 40 minutes.
- After 40 minutes, remove the casserole from the oven, sprinkle with Gruyere cheese and put it back in for another 10 minutes or until the cheese melts and turns brown.
- Let it cool before serving.
Frequently Asked Questions
This recipe is vegetarian, not vegan. It uses butter, liquid cream, and Gruyere cheese, which are all dairy products. If you follow a strict vegetarian diet, look for a Gruyere or an alternative cheese made with vegetarian (non-animal) rennet.
No. The sweet potatoes are sliced thin on a mandoline and cook fully in the oven. Baking them covered in warm cream for 40 minutes softens them all the way through, so there is no need to pre-boil.
Gruyere gives a deep, nutty flavor, but Comte or Emmental are close Alpine cheeses that melt and brown in a similar way. Any good semi-hard melting cheese will work if that is what you have on hand.
Watery gratin usually comes from slices that are too thick or from serving it right out of the oven. Slice the sweet potatoes thin and even, and let the dish rest for a few minutes so the cream thickens and sets around the potatoes before you cut into it.
Yes. You can assemble it a few hours ahead and refrigerate it covered, then bake when ready. Cooked leftovers keep in an airtight container in the fridge for up to three days and reheat well in a covered dish in the oven.
Sage is steeped in the warm cream off the heat for 5 to 10 minutes, which infuses the cream with a savory, earthy aroma. That herbal note balances the natural sweetness of the sweet potatoes and the richness of the cheese.
