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French Onion Soup Potato Bake: Cheesy Comfort Casserole

Close-up of a rich, cheesy french onion soup potato bake with a deeply browned, herbed crust.
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Create a hearty potato bake that captures the deep, savory flavors of classic French Onion Soup, featuring caramelized onions, rich broth, and a thick, bubbly Gruyère topping.

Ingredients

Scale
  • 3 lbs Russet potatoes, peeled and thinly sliced (about 1/8 inch thick)
  • 4 large yellow onions, thinly sliced
  • 4 tablespoons unsalted butter
  • 1 teaspoon salt, divided
  • 1/2 teaspoon black pepper, divided
  • 2 tablespoons all-purpose flour
  • 1 cup dry red wine (optional, substitute with broth)
  • 4 cups rich beef broth
  • 1 tablespoon Worcestershire sauce
  • 1 teaspoon fresh thyme leaves
  • 1 cup heavy cream
  • 8 ounces Gruyère cheese, shredded
  • 4 ounces Swiss cheese, shredded

Instructions

  1. Prepare the Onions: Melt the butter in a large, heavy-bottomed pot or Dutch oven over medium heat. Add the sliced onions and 1/2 teaspoon of salt. Cook slowly, stirring occasionally, for 30 to 40 minutes until the onions are deeply browned and caramelized. This slow process builds the flavor.
  2. Build the Sauce Base: Sprinkle the flour over the caramelized onions and stir for 1 minute. If using wine, pour it in and scrape up any browned bits from the bottom of the pot. Let it simmer until reduced by half, about 3 minutes.
  3. Simmer: Pour in the beef broth, Worcestershire sauce, thyme, remaining 1/2 teaspoon salt, and 1/2 teaspoon pepper. Bring the mixture to a simmer and cook for 5 minutes, allowing the flavors to combine. Remove from heat and stir in the heavy cream.
  4. Assemble the Bake: Preheat your oven to 375 degrees Fahrenheit. Lightly grease a 9×13 inch baking dish. Arrange one-third of the thinly sliced potatoes in an even layer on the bottom of the dish.
  5. Layer: Pour half of the onion and broth mixture evenly over the potatoes. Top with one-third of the combined Gruyère and Swiss cheese. Repeat the layering process: potatoes, remaining onion mixture, potatoes, and then the remaining cheese mixture.
  6. Bake: Cover the baking dish tightly with aluminum foil. Bake for 45 minutes.
  7. Finish Baking: Remove the foil and continue baking for another 20 to 25 minutes, or until the potatoes are tender when pierced with a fork and the cheese topping is melted, bubbly, and golden brown.
  8. Rest: Let the French Onion Potato Casserole rest for 10 minutes before serving.

Notes

  • For a vegetarian version, substitute the beef broth with a rich, dark vegetable broth or mushroom broth.
  • If you want to make this ahead, assemble the entire casserole (without baking) and cover it tightly. Refrigerate for up to 24 hours. Add 15 minutes to the initial covered baking time if baking directly from the refrigerator.
  • Thinly sliced potatoes cook more evenly, similar to a Gratin Dauphinois. Use a mandoline if you have one for uniform thickness.

Nutrition

Find it online: https://tastethisplate.com/french-onion-soup-potato-bake/