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Caramelized Onion and Potato Gratin

Potato Gratin in a light blue baking dish.

A rich and heavenly potato gratin with caramelized onions and a thick layer of gruyere cheese on top. Caramelized Onion and Potato Gratin  is one side dish everyone will love. This time of year I can never get enough of creamy, starchy casseroles. Cold, bleak weather calls for pure comfort food.

And speaking of cold weather, can you believe it is December already? Where did the previous 11 months go? I haven’t even bought a single Christmas present yet. And I may keep it that way because this year, with all my family has been through, I have no interest in anything material. I just want to be surrounded by family, with lots of good food of course.

Caramelized Onion and Potato Gratin in blue baking dish with plates and spoon beside it.

And this potato gratin is definitely good food to have on hand, for a holiday, a family gathering, or a Sunday supper. This recipe was published in the October/November 2010 issue of Cook’s Country, a magazine I always find to be a reliable source for recipes. I’ve added a few sweet potatoes, mainly because I put them in absolutely everything I can. But if you object to sweet potatoes (like the majority of my family does) just use russet potatoes.

Serving of Gratin on a plate.

It’s best to use a mandolin to slice the potato slices really thin unless you have an extraordinary talent for thinly and uniformly slicing potatoes by hand. I’m always surprised at how long it takes for the potatoes in a gratin to cook all the way and if you have unevenly sliced potatoes you are bound to have a crunch here and there in your gratin.

The caramelized onions cook up really fast with the addition of some brown sugar. I love that the onions are chopped instead of sliced. They really blend into the casserole better that way and you don’t have any awkward onion strings dangling down from your fork.

Serving of potato gratin on a plate.

Caramelized Onion and Potato Gratin topped with gruyere cheese.

Caramelized Onion and Potato Gratin

A creamy, cheesy potato gratin flavored with caramelized onions and fresh thyme.


  • 2 tablespoons unsalted butter
  • 3 cups chopped onions, about 2 large or 3 medium
  • 2 teaspoons salt
  • 1 tablespoon brown sugar
  • 1 cup low-sodium chicken broth
  • 2/3 cup white wine
  • 2/3 cup heavy cream
  • 1 teaspoon balsamic vinegar
  • 3 pounds russet potatoes, I used a combo of russets and sweet potatoes, peeled and sliced 1/8-inch thick
  • 2 teaspoons minced fresh thyme
  • 1 teaspoon pepper
  • 1 1/2 cups shredded Gruyere cheese


  • Position an oven rack in the middle of oven and heat oven to 350 degrees.
  • Melt butter in a large nonstick skillet over medium-high heat. Add onions and 1 teaspoon salt. Cook until onions are just starting to brown, about 5 minutes.
  • Stir in brown sugar and continue to cook for about 5 minutes, stirring frequently. Onions should be golden brown.
  • Add 1/3 cup broth and cook 5 additional minutes. Mixture should be golden brown and sticky. Transfer onions to medium bowl.
  • Add remaining broth plus wine, cream, and remaining 1 teaspoon salt to skillet and bring to a boil. Scrape any browned bits off bottom. Once at a boil, remove from heat and stir in vinegar. Cover and keep warm.
  • In a 3-quart casserole dish, arrange half of potatoes so that they are overlapping. Sprinkle with 1 teaspoon thyme and 1/2 teaspoon pepper.
  • Spread all of caramelized onions on top.
  • Top with remaining potatoes, thyme, and pepper. Pour broth mixture over the top.
  • Place in oven and bake 30 minutes. Remove from oven and top with cheese. Place back in oven for 30 to 40 minutes. Let cool 15 minutes before serving.
Course: Side Dish

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Caramelized Onion and Potato Gratin topped with gruyere cheese.

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13 thoughts on “Caramelized Onion and Potato Gratin”

  1. Very good recipe! It was a hit at our Christmas Eve gathering. Everyone wanted to take some home.

  2. I can’t believe it’s December already too. My favorite part of the holidays is definitely getting to spend quality time with loved ones as well.
    This potato gratin looks wonderful Christin, I love that you added some sweet potatoes in here – sounds delicious 🙂

  3. Amy @ Elephant Eats

    I seriously can’t believe December is already here…time really is going by too quickly. Mmmm, what a perfect comfort food on these cold nights 🙂 I really need a mandoline slicer so I can whip this up! Maybe i’ll add it to my chrismas list 😉

    1. Christin
      Christin Mahrlig

      The time is definitely gong by too fast! I’m going to become one of those crazy people who doesn’t even bother to put their decorations away.

  4. Ashley @ Wishes and Dishes

    I’m in disbelief that it’s December, too!!! What happened to 2013?? Love this dish….I could eat something like this for every meal LOL

  5. I’m with you — I haven’t bought any gifts yet, and I couldn’t care less. The holidays are more about being with family and enjoying great food than getting gifts. I like giving homemade gifts, but that’s it! This gratin looks so perfect as a side for any meal, and I love the sound of all of those ingredients!

  6. Consuelo @ Honey & Figs

    You’re right, family, friends (and good food!) are way better than anything material! I hope you and your family enjoy Christmas after all.
    And waht a wonderful gratin! I’m definitely adding those sweet potatoes, I bet they make this super delish 🙂

  7. easyfoodsmith

    Potato gratin is one of my favorite dishes and I love to have with toasted garlic bread. Your dish has comfort written all over it. I am bookmarking your recipe to try it soon.

  8. easyfoodsmith

    Potato gratin is one my favorite dishes and I love to have with toasted garlic bread. Your dish has comfort written all over it. I am bookmarking your recipe to try it soon.

  9. ATasteOfMadness

    Oh wow. I just made roast potatoes, but I wish I saw this first. This looks SO good!!

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