French Onion Soup Potato Gratin

It’s Thanksgiving time which means it’s time to start planning those Thanksgiving day menus! There’s turkey, of course, soup, side dishes, desserts and lots and lots of snacks. While I don’t eat much of the meat these days, I absolutely love the side dishes. They are truly my favorite.

Instead of making my Easy, Creamy Mashed Potatoes, this year, I’ve decided I wanted make some kind of extra special, decadent potato dish. Something creamy, something cheesy, something delicious!

While I was looking for the perfect recipe, I put on the Kitchn to watch their Thanksgiving day special and there it was! My dreamy potato dish I was looking for. The only catch is theirs used more meaty things in it, so with a few changes, I made an amazing, fully vegetarian, potato dish. It’s all sorts of creamy, full of cheese flavor and the onions – the ONIONS – they make it over the top! They are honestly my favorite part! They taste just like the ones from my French Onion Soup but even better!

Definitely make sure you leave time to make this one. It does take a while but it’s BEYOND worth it.

Happy Thanksgiving to you and your family! Happy Cooking!img_1628_jpg

French Onion Soup Potato Gratin

  • Servings: 8-10
  • Difficulty: medium
  • Print


Caramelized Onions:

  • 8 tablespoons unsalted butter
  • 5 large yellow onions, sliced 1/4 inch thick
  • Kosher salt and freshly ground black pepper
  • 3/4 cup veggie stock
  • 2 teaspoons Dijon mustard

Potato Gratin:

  • 3 pounds Russet potatoes
  • Kosher salt and freshly ground black pepper
  • 8oz Gruyere, shredded
  • 4 ounces mozzarella, shredded
  • 1 cup heavy cream
  • 1 cups veggie stock
  • One 4 1/2-ounce bag premade croutons, lightly crushed
  • One 3 1/2-ounce bag French fried onions


  1. For the caramelized onions: In a large saucepan over medium-high heat, melt the butter. Once melted and bubbling, add a large handful of the onions and cook until translucent, 1 to 2 minutes. Repeat until all the onions have been added. Season with a pinch of salt and black pepper. Reduce the heat to low and cook, stirring occasionally, until the onions turn medium brown, about 30 minutes. If the onions start to get too dark, add 1 to 2 tablespoons of stock as necessary. Add the mustard and stir to coat. Season with salt and pepper. Remove from the heat and set aside.img_1575_jpg
  2. For the potato gratin: Preheat the oven to 400 degrees. Lightly grease the bottom and sides of a large (12-inch) cast-iron skillet.
  3. Using a sharp knife, cut the potatoes into thin slices. Arrange a thin shingled layer of potatoes in a circle around the skillet. Season the potatoes with salt and pepper, then arrange an even layer of caramelized onions on top of the potatoes. Season with salt and pepper.img_1599
  4. In a medium bowl, combine the Gruyere and mozzarella and reserve half for later use. Sprinkle on a layer of the remaining cheese mixture over the onions. Repeat the layers until all the ingredients (not including the reserved cheese) have been used. Press down firmly on the layers to flatten.
  5. In a large bowl or measuring cup, combine the heavy cream and stock and pour over the gratin. Cover the skillet with foil and place on a sheet pan. Bake the potatoes, covered, until the top and edges have begun to brown and the potatoes are tender, 1 hour 15 – 1 hour 30 minutes. You can test by inserting a knife into the potatoes; if it goes in and comes out without resistance, then the potatoes are done.img_1609
  6. Remove the skillet from the oven, remove the foil and turn the broiler on high. Combine the croutons and French fried onions. Cover the gratin with a layer of the crouton mixture followed by the remaining cheese. Broil until golden brown and bubbly, 5 to 8 minutes.img_1620
  7. Remove from oven and let cool slightly before serving. Enjoy!img_1628_jpg

 Original recipe can be found here

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