Sweet Potato Gratin

Sweet Potato Gratin Recipe

This sweet potato gratin is not your grandma’s potato gratin. (And by that we mean no disrespect to anyone’s grandma. We love grandmas. In particular little French grandmas who take to their local fromagerie for Gruyère when they make gratin and who toss it together without measuring or weighing but just by knowing.)–Renee Schettler Rossi

LC Thinly Sliced Spuds Note

We started to wonder, while editing this sweet potato gratin recipe, what our dear readers prefer to reach for when it come time to slice a lotta spuds. A food processor? A mandoline? A paring knife? Go on. Let us know in a comment below.

Sweet Potato Gratin Recipe

  • Quick Glance
  • 45 M
  • 2 H
  • Serves 4


  • Unsalted butter, for the baking dish
  • 1 cup (8 ounces or 250 milliliters) heavy cream
  • 1 cup low-sodium homemade vegetable or chicken broth
  • 2 cloves garlic, peeled and mashed
  • 4 sage leaves, torn in half
  • Salt and freshly ground white or black pepper
  • 2 pounds (1 kilogram) sweet potatoes, preferably garnet
  • 2 russet potatoes (about 1 1/2 pounds)
  • 1/2 cup (2 ounces or 60 grams) shredded Parmesan
  • 1/2 cup (2 ounces or 60 grams) shredded Gruyère cheese


  • 1. Preheat the oven to 375°F (190°C). Butter the bottom and sides of a 9-by-13-inch (23-by-33-centimeter) or a 3-quart (3-liter) baking dish with butter.
  • 2. In a small saucepan, combine the cream, broth, garlic, sage, and a good pinch of salt and pepper over medium-low heat and heat until small bubbles begin to appear around the edge of the pan and the liquid is steaming, 10 to 15 minutes. Remove from the heat and let steep while you prepare the potatoes.
  • 3. Cut the rounded ends off each potato, then peel the potatoes. Using a food processor or mandoline fitted with the slicing blade, cut the potatoes crosswise into slices 1/4 inch (6 millimeters) thick. Layer the potato slices, alternating types, in the prepared baking dish. Pour the warm cream mixture through a fine-mesh sieve evenly over the potatoes and discard the garlic and sage. Cover the dish tightly with foil and bake for 45 minutes.
  • 4. In a small bowl, toss together the Parmesan and Gruyère cheeses.
  • 5. Uncover the potatoes and sprinkle with the cheeses. Continue to bake, uncovered, until the mixture is bubbly and thick, 25 to 30 minutes. Let stand for 10 minutes before serving.
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Recipe Testers Reviews

Recipe Testers Reviews
Testers Choice
Pat Francis

Nov 14, 2015

A pretty, cheesy casserole. The final sweet potato gratin was tender and delicious, not to mention attractive. It made a wonderful dish for a fall weekend dinner. However, the time investment probably renders it less suitable to many households for a weeknight. It took longer than the time given in the recipe for the potatoes to be cooked through and the casserole to be sufficiently browned on top. A little extra time invested was worth it in the end. As I was slicing the potatoes, I realized there would be more sweet potato slices than russet ones, so I didn’t use the last sweet potato. I used 22 1/2 ounces sweet potatoes, which was more in line with the amount of russets. The combined potatoes filled the casserole dish nearly to the top. The shapes of the potatoes were also divergent. I couldn't find any fat garnet yams, so the slices were not as uniform as I would have liked. I salvaged the leftover sage and garlic from the simmered sauce to use in a pan sauce for pork chops that accompanied the gratin.

Testers Choice
Chiyo Ueyama

Nov 14, 2015

This sweet potato gratin is a straightforward recipe that yields a delicious and satisfying dish—a winner. I loved the subtlety of all the players in the gratin, which allowed the sweet potatoes to shine, as you would rightly expect from the name. The garlic and sage weren’t overpowering, and the combination of chicken broth and cream made a sauce that thickened perfectly at the end and wasn’t overly rich. The amounts for the cheeses were spot-on as well. If you don’t care for sage, I think fresh thyme or tarragon would be a lovely alternative. The attractive gratin with alternating colors of russet and sweet potatoes can be part of a holiday table or a casual supper on a weeknight.

Testers Choice
Irene Seales

Nov 14, 2015

Simple and perfect. This recipe works for company and holidays and is also so simple to pull together just for two, which is what we did.The recipe halves perfectly, and we had it one night as part of dinner and easily reheated the rest for weekend brunch. I used a 2-quart Emile Henry oval dish. The flavor of the infused sage and garlic is light and delicate but worked especially well with a nutty, aged Comté, which we used instead of Gruyère, and the Parmesan. Love that the cheese was specified in weight. The recipe takes a bit of active time. While your oven is heating, you can prep the potatoes, make the sauce, and be ready to put it in the oven in 20 minutes. You have plenty of time to prep your cheese during the first baking phase. I found it needed the full 30 minutes to brown at the end. Honestly, this is such a low-stress recipe with such a clean flavor, I really wouldn’t change a thing next time. No floury sauce, no extra butter, and it would be easy to keep vegetarian by using vegetable broth in place of chicken stock and carefully selecting your cheese. If I had made a full recipe, I would probably have used 2 oval dishes because they are easy to pass at the table or on a buffet and look so nice. 

IF (big IF) you have leftovers, they reheat beautifully at 350℉ under foil for 20 to 30 minutes. Winner winner!

Testers Choice
Linda Pacchiano

Nov 14, 2015

We really enjoyed this novel sweet potato gratin with its combination of sweet and russet potatoes. It's a dish I'm planning to make for Thanksgiving because it will save me the trouble of making two potato dishes to satisfy the preferences of sweet potato lovers and white potato lovers. Even my husband, who does not care for sweet potatoes, enjoyed this dish. I followed the recipe exactly, however, I feel you could change the ratio of sweet to white potatoes to suit your own preference. Or you could make it with just one or the other type of potato. The food processor is definitely the way to go for slicing the potatoes. Normally, I would use my mandoline, but the sweet potatoes are too hard to allow for smooth slicing. The russets will slice quite easily on a mandoline, but I used the food processor slicer for them, too.

Testers Choice
Natalie Reebel

Nov 14, 2015

This sweet potato gratin was a hit at my home. While the sauce warms and steeps, the aroma drifting through the house is truly delightful and builds anticipation. The potatoes emerge from the oven tender with a creamy sauce and nicely browned top, a beautiful dish worthy of the weekend or the holiday table. The beauty of it is also how simple it is to put together. The potatoes cooked perfectly in the times given in the recipe. The one recommendation I would make for this recipe would be to add more salt, say 1/2 to 3/4 teaspoon, to the sauce. The finished dish was a touch under-seasoned for us.

Testers Choice
Ralph Knauth

Nov 14, 2015

A perfect side dish for any roast. Easy, great to prep in advance, colorful. A keeper. This recipe worked extremely well and tasted even better. Everybody loved it. I prepared only half of it, since we were only 3 people, in an oval 9-inch dish, which worked very well. To cut the potatoes, I used a chef's knife. No use in dirtying a Cuisinart. I made some minor changes, intentionally and unintentionally. Since I was out of Gruyère, I used a Teleme cheese, which is somewhat similar to mozzarella and worked great! Furthermore, I bought orange "sweet potatoes," which looked great layered with the russets, but later learned from my produce guy that they were actually red yams. Whatever they're called, they tasted good!

  1. Martha in KS says:

    I use a cheap mandoline for slicing potatoes, onions, apples & similar foods. I used it yesterday to make shards of parmesan for a salad. It does a great job as long as you watch out & don’t lose any fingertips!

  2. To slice anything that isn’t shaved, I find a really sharp knife does the trick. For something shaved (like fresh fennel), I have an old slicer my mother used and it’s crazy sharp, easily adjusted, very basic, but does the trick. I do use mandolines for some things, but I’m not fond of the food processor for slicing, because the food I’m trying to slice never seems to fit the chute. Don’t you just hate when that happens?

    • Beth Price says:

      I do hate that, gourmet goddess. I have two processors, a new-fangled one with a chute the size of a carrot and and old circa-1980s with a chute the size of a sweet potato. Guess which one I use most?

  3. Mamuka says:

    For me the mandoline is the answer. I use it all the time when slicing lots especially when I want them sliced really thin and uniform. Used to use a knife, but the mandoline saves time.

    • Renee Schettler Rossi says:

      Mamuka, sounds perfect. I consider my mandoline indispensable, too. Many thanks for taking the time to chime in!

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