Caramelized Onion Potato Gratin

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Give me all the gratins please!! This Cheesy Potato Gratin is one for the record books and you need it STAT.

Cheesy Potato Gratin from (@Whatsgabycookin)


I mean, what's not to love about thinly sliced potatoes layered with caramelized onions, heavy cream, tons of cheese, herbs, salt and pepper? It's basically the most magical side dish on the planet. And I am NOT to be left alone with it.  Somehow this Cheesy Potato Gratin always disappears very quickly and I don't want to be held accountable.

This will be making an appearance on my holiday dinner party table this year and I am 100% confident in saying you should be doing the same. TRUST. It's the best. Potato Gratin for EVERYONE.

Cheesy Potato Gratin from (@Whatsgabycookin)

If you tried this recipe, please leave a 🌟 star rating and let me know how it goes in the 📝 comments below. Thanks for visiting today

Cheesy Potato Gratin from (@Whatsgabycookin)

Cheesy Potato Gratin

Author: Gaby Dalkin
5 from 22 votes
Give me all the gratins please!! This Cheesy Potato Gratin is one for the record books and you need it STAT.
Prep Time 10 minutes
Cook Time 1 hour 10 minutes
Total Time 1 hour 20 minutes
Course Side Dish
Cuisine French
Servings 8 people


  • 2 pounds Yukon Gold potatoes (Russet potatoes also work as do sweet potatoes or a combination of any of the above)
  • Kosher salt and freshly ground pepper
  • 1 tablespoons olive oil
  • 1 yellow onion diced
  • 1 ½ cups heavy cream
  • 1 cup shredded Gruyère cheese
  • ¾ cup shredded parmesan cheese
  • ¼ cup crème fraîche or mascarpone cheese
  • Fresh thyme for garnish


  • Preheat an oven to 400°F. Grease a 9-inch baking dish with butter or non-stick cooking spray.
  • Cut the potatoes into ⅛ inch slices. Arrange the slices, slightly overlapping, on the bottom of the baking dish and season with salt and pepper.
  • In a medium skillet, heat the olive oil over medium high heat. Add the onion and sauté until starting to caramelize, about 8-10 minutes. Add the heavy cream and bring the liquid to a simmer. Simmer until slightly thickened, about 5 minutes. Stir in ¾ cup of the gruyere cheese and all of the parmesan and cook until smooth and melted. Remove the mixture from the heat, let cool slightly and stir in the crème fraîche. Season with salt and pepper.
  • Pour the cream mixture evenly on top of the potatoes and sprinkle the remaining ¼ cup of Gruyere cheese evenly on top. Bake until golden brown and bubbly and the potatoes are fork tender when pierced with a knife, about 45 minutes to 1 hour. Let the gratin rest for about 15-30 minutes before serving. Garnish with thyme and serve.


I recommend learning to use a mandolin. With the safety features and patience you can easily cut even slices without getting your fingers.

Nutrition Information

Calories: 379kcal | Carbohydrates: 23g | Protein: 12g | Fat: 27g | Saturated Fat: 16g | Polyunsaturated Fat: 1g | Monounsaturated Fat: 8g | Cholesterol: 79mg | Sodium: 290mg | Potassium: 571mg | Fiber: 3g | Sugar: 3g | Vitamin A: 933IU | Vitamin C: 24mg | Calcium: 331mg | Iron: 1mg
Tried this Recipe? Tag me Today!Mention @WhatsGabyCookin or tag #whatsgabycooking!


  1. How long would you par-bake this to prepare a day ahead? How long to cook before serving? Thank you

    1. you could assemble the day ahead and par bake it for 30 minutes and then finish the day of

  2. 5 stars
    This turned out delicious! Definitely will make again! The family loved it! Added minced garlic cloves.

  3. If you are making a day ahead, can you cook all the way through and reheat the next day? Or is best to par-bake and finish cooking through day of?

  4. Hi

    The equipment list references a 9x13 baking dish while the recipe mentions a 9 inch dish. I wasn’t sure if this meant 9 inch square or if it is indeed a 9x13


  5. Can you make this a day ahead and reheat in the oven or would it be to dry the next day? Thanks! Love all your recipes!

  6. 5 stars
    This was a HUGE hit at Christmas dinner. So easy to prepare (with the help of a mandoline to thinly and evenly slice potatoes). Thanks for this recipe, Gaby!

  7. 5 stars
    I made this for Christmas dinner as an accompaniment to beef tenderloin with red wine sauce. I may have received the most compliments ever from my husband and we’ve been married 36 years! Thanks for a wonderful recipe.

  8. I see that you can make a day ahead, can you make two days ahead and still apply the par-bake method? Thanks and happy holidays!

  9. 5 stars
    Made these TWICE for Thanksgiving and Friendsgiving and they were excellent! The cheesy, decadent dish you want for the holidays!

  10. Gaby,
    Wildly into menu planning for a turkey-less dinner.
    Committed to Duck breast, Mushroom Bread Pudding, Miso honey brussels sprouts, arugula anchovy salad, some kind of cranberry sauce and here's the 64k question:

    Gaby's Potatoes Au Gratin or your Sweet Potato Gratin (or??????)
    Does the bread pudding do battle with the white potatoes? What do you think?
    Ask Poppy?
    Best wishes to you and yours!

  11. I lost what happens to the onions. Leave them in the pan when you add cream and cheeses? I don’t see onions in the top of the potatoes from pouring the mixture over the top of them.

5 from 22 votes (6 ratings without comment)

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