Hey y'all! If you love the classic flavors of French onion soup and crave cheesy, melt-in-your-mouth comfort food, this French Onion Potatoes au Gratin is about to become your new favorite. Golden potatoes layered with caramelized onions, creamy sauce, and bubbling cheese make this the ultimate side for holiday dinners, potlucks, or any night you want to impress. Let’s get cooking!
Why You'll Love This French Onion Potatoes au Gratin
- The perfect blend of sweet caramelized onions and rich, gooey cheese in every bite.
- Great for holidays, family dinners, or comforting Sunday meals.
- It’s naturally vegetarian and can be easily adapted for gluten-free diets.
- Easy, make-ahead friendly—just reheat and enjoy!
- Pairs beautifully with a variety of main courses.
Ingredients for French Onion Potatoes au Gratin
- 2.5 lbs (about 1.1 kg) Yukon Gold potatoes, thinly sliced
- 2 large yellow onions, thinly sliced
- 3 tablespoon unsalted butter
- 1 tablespoon olive oil
- 2 cloves garlic, minced
- 1 teaspoon fresh thyme leaves (or ½ teaspoon dried thyme)
- 1 ½ teaspoon kosher salt, divided
- ½ teaspoon freshly ground black pepper
- 1 cup (240 ml) heavy cream
- 1 cup (240 ml) whole milk
- ½ teaspoon Dijon mustard
- 2 cups (200g) Gruyère cheese, grated
- ½ cup (50g) Parmesan cheese, grated
- Fresh parsley, chopped (optional, for garnish)
How to Make French Onion Potatoes au Gratin
Step 1: Caramelize the Onions
- In a large skillet, heat butter and olive oil over medium heat. Add sliced onions and cook, stirring often, until golden and deeply caramelized, about 25-30 minutes. (Add a splash of water if onions begin to stick.)
- Stir in the garlic, thyme, and ½ teaspoon salt. Cook for 2 more minutes, then remove from heat.
Step 2: Prepare the Creamy Sauce
- In a medium bowl, whisk together the cream, milk, Dijon mustard, 1 teaspoon salt, and black pepper until combined.
Step 3: Layer and Assemble the French Onion Potatoes au Gratin
- Preheat your oven to 375°F (190°C) and grease a 9x13-inch (23x33cm) baking dish.
- Layer half the potatoes in the bottom of the dish, overlapping slightly. Top evenly with half the caramelized onions, half the Gruyère, and half the Parmesan.
- Repeat with the remaining potatoes, onions, and cheese.
- Pour the cream mixture evenly over the top.
Step 4: Bake
- Cover the dish tightly with foil and bake for 40 minutes.
- Remove foil and bake an additional 20-25 minutes, or until the top is golden brown and potatoes are fork-tender.
- Let rest for 10 minutes before serving. Garnish with parsley, if desired.
Notes for the Best French Onion Potatoes au Gratin
- Slicing the potatoes evenly ensures consistent cooking; using a mandolin can help. (Learn potato slicing tips)
- Don't rush caramelizing the onions—low and slow brings out the best flavor.
- For extra cheesy goodness, broil for 2-3 minutes at the end (watch closely!).
French Onion Potatoes au Gratin Variations
- Mushroom Twist: Add 1 cup of sautéed cremini mushrooms with the onions for an earthy flavor.
- Meaty Version: Stir in 1 cup of chopped cooked bacon or ham between layers.
- Gluten-Free: Ensure your cheeses and Dijon are certified gluten-free; swap cream for a non-dairy version if needed.
What You’ll Need: Equipment for French Onion Potatoes au Gratin
- Large skillet or sauté pan
- Whisk and mixing bowls
- Mandolin (optional, for slicing potatoes)
- 9x13-inch baking dish
- Sharp knife
- Aluminum foil
Storage & Shelf Life for French Onion Potatoes au Gratin
Cool completely, then cover and refrigerate leftovers for up to 4 days. To reheat, cover and bake in the oven at 325°F (160°C) until heated through, about 20 minutes. For longer storage, freeze baked and cooled gratin in airtight containers for up to 2 months; thaw overnight before reheating.
Pairings & Serving Suggestions for French Onion Potatoes au Gratin
- Serve alongside roast chicken, steak, or baked salmon.
- Pair with green vegetables like steamed broccoli or a crisp green salad.
- Enjoy as a stand-alone main with a side of crusty baguette.
Pro Tips for Perfect French Onion Potatoes au Gratin
- Use Yukon Gold or Russet potatoes for their creamy texture and ability to hold their shape. (Read more on potato types here).
- Let the gratin rest after baking so the sauce thickens and it slices neatly.
- Sprinkle a bit of extra cheese on top during the last 5 minutes of baking for a truly golden crust.
FAQ: French Onion Potatoes au Gratin
- Can I make French Onion Potatoes au Gratin ahead of time?
- Absolutely! Assemble it 1 day in advance, store covered in the fridge, then bake when ready to serve.
- Can I use a different cheese?
- Yes—Swiss, Emmental, or sharp white cheddar work well if you don’t have Gruyère.
- How can I lighten up this recipe?
- Swap half-and-half or whole milk for some of the cream, and use reduced-fat cheeses as desired (try a lighter gratin here).
Prep Time: 25 minutes
Cook Time: 1 hour 10 minutes
Total Time: 1 hour 35 minutes
Ingredients
- 2 lbs russet potatoes, thinly sliced
- 2 large yellow onions, thinly sliced
- 2 cups Gruyère cheese, grated
- 1 cup Swiss cheese, grated
- 2 cups heavy cream
- 3 tablespoon unsalted butter
- 1 tablespoon olive oil
- 1 teaspoon fresh thyme leaves
- Salt and black pepper, to taste
Instructions
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1Preheat the oven to 375°F (190°C). Butter a 9x13-inch baking dish.
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2In a large skillet over medium heat, melt butter with olive oil. Add onions and cook, stirring occasionally, until deeply caramelized and golden brown, about 20 minutes. Stir in thyme leaves and season with salt and pepper.
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3Layer half of the sliced potatoes in the prepared dish. Top with half the caramelized onions and sprinkle with half the Gruyère and Swiss cheese.
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4Repeat with remaining potatoes, onions, and cheese. Pour the heavy cream evenly over the top.
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5Cover with foil and bake for 40 minutes. Remove foil and bake another 20 minutes, or until golden and bubbling. Let cool slightly before serving.
Approximate Information for One Serving
Nutrition Disclaimers
Number of total servings shown is approximate. Actual number of servings will depend on your preferred portion sizes.
Nutritional values shown are general guidelines and reflect information for 1 serving using the ingredients listed, not including any optional ingredients. Actual macros may vary slightly depending on specific brands and types of ingredients used.
To determine the weight of one serving, prepare the recipe as instructed. Weigh the finished recipe, then divide the weight of the finished recipe (not including the weight of the container the food is in) by the desired number of servings. Result will be the weight of one serving.
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