Save My neighbor knocked on the door one Thursday evening with a crumpled magazine page showing French onion soup. She wanted to make it vegetarian for her daughter but still keep that deep, savory richness. We stood in my kitchen brainstorming, and when I pulled out a bag of potatoes, something clicked. What if we turned those flavors into something you could actually serve alongside dinner? That night, we caramelized onions until the whole house smelled like a Parisian bistro, piled them onto golden roasted potatoes, and buried everything under a blanket of Gruyère.
I made this for a small dinner party in February, and everyone kept asking what smelled so good while it baked. When I brought the dish to the table, the cheese was still bubbling, and the edges of the potatoes had crisped up again in the oven. One friend took a bite and said it tasted like the coziest winter evening she could imagine. We ended up eating straight from the baking dish, passing it around with forks, because no one wanted to wait for plating.
Ingredients
- Yukon Gold or russet potatoes: Yukon Golds give you a buttery flavor and hold their shape beautifully, while russets get crispier on the edges if you like more texture.
- Yellow onions: These caramelize into pure sweetness over low heat, forming the soul of this dish.
- Unsalted butter and olive oil: The combination keeps the onions from burning while adding richness.
- Fresh thyme: This herb belongs in anything inspired by French onion soup.
- Balsamic vinegar: Just a teaspoon deepens the onions and adds a subtle tang that balances the sweetness.
- Gruyère cheese: It melts into stretchy, nutty perfection and tastes like the top of a proper French onion crock.
- Parmesan cheese: Optional, but it adds a salty sharpness that makes the topping even better.
- Fresh parsley: A handful of green at the end brightens everything up and makes it look like you tried.
Instructions
- Roast the potatoes:
- Preheat your oven to 220°C (425°F) and line a large baking sheet with parchment paper. Toss the potato slices with olive oil, salt, and pepper, then spread them out so they are not crowded. Roast for 25 to 30 minutes, flipping halfway through, until the edges turn golden and the centers are tender when poked with a fork.
- Caramelize the onions:
- While the potatoes roast, heat butter and a tablespoon of olive oil in a large skillet over medium low heat. Add the sliced onions and a pinch of salt, then stir every few minutes as they slowly turn golden and sweet, about 25 to 30 minutes. Stir in the thyme and balsamic vinegar during the last couple of minutes, then remove from heat.
- Assemble and bake:
- Lower the oven temperature to 200°C (400°F). Arrange the roasted potato slices in a lightly greased baking dish, overlapping them slightly like roof shingles. Spoon the caramelized onions evenly over the potatoes, then sprinkle the grated Gruyère and Parmesan on top. Bake for 10 to 15 minutes until the cheese is melted, bubbling, and starting to brown in spots.
- Garnish and serve:
- Let the dish cool for a few minutes so the cheese sets just a bit. Scatter chopped fresh parsley over the top and serve warm, preferably while everyone is still gathered around the table.
Save A few weeks after that first test run, I brought this to a potluck where half the people were vegetarian and the other half were dedicated meat eaters. The dish disappeared in under ten minutes. Someone asked if I had catered it, and I just laughed because I had made the whole thing in my tiny apartment kitchen while listening to a podcast. It felt good to know that something this simple could make people that happy.
Make Ahead Magic
You can caramelize the onions up to three days in advance and store them in the fridge in an airtight container. When you are ready to serve, just roast the potatoes, assemble everything, and bake. I have also fully assembled the dish a few hours ahead, covered it with foil, and kept it in the fridge until it was time to pop it in the oven. Just add five extra minutes to the baking time if you are starting from cold.
Swaps and Variations
If you cannot find Gruyère, Swiss cheese works beautifully and melts just as well. For a little extra punch, stir a splash of dry white wine into the onions after they have caramelized. You can also use red onions for a slightly sweeter, more colorful result, though yellow onions give you that classic French onion flavor. If you want to make this vegan, swap the butter for more olive oil and use a plant based cheese that melts well.
Serving Suggestions
This dish shines next to a simple roast chicken, a seared steak, or even a pile of sautéed greens. It is hearty enough to serve as a vegetarian main course if you pair it with a crisp green salad dressed in lemon vinaigrette. I have also served it at brunch alongside scrambled eggs, and it felt like the fanciest thing on the table.
- Pair with roasted vegetables or a arugula salad for a lighter meal.
- Serve it family style in the baking dish so everyone can dig in.
- Leftovers reheat beautifully in the oven at 180°C (350°F) until warmed through and the cheese gets melty again.
Save This recipe has become one of those dishes I make when I want something comforting but a little special, without spending hours in the kitchen. Every time I pull it out of the oven, I am reminded that the best food does not need to be complicated, it just needs to taste like you care.
Recipe Q&A
- → Can I prepare this dish ahead of time?
Yes, you can roast the potatoes and caramelize the onions up to 8 hours ahead. Assemble the dish just before baking to keep potatoes from absorbing excess moisture. This makes it convenient for entertaining.
- → What's the best way to caramelize onions properly?
Use medium-low heat and stir often to prevent burning. The process takes 25–30 minutes and requires patience—this slow cooking develops the deep golden color and sweet flavor. Resist the urge to increase heat, as it affects the final taste.
- → Can I use different potato varieties?
Yukon Gold and russet potatoes work best for this dish. Waxy potatoes like red potatoes may not crisp as well. Choose starchy varieties for optimal texture and golden browning during roasting.
- → What cheese alternatives work if I don't have Gruyère?
Swiss cheese, Emmental, or aged Cheddar are excellent substitutes with similar melting properties. Avoid soft cheeses that don't brown as beautifully. Parmesan can enhance any choice with additional depth.
- → How do I ensure the cheese bubbles perfectly?
Grate the cheese freshly rather than using pre-shredded varieties, which contain anti-caking agents that prevent smooth melting. Bake at 400°F for 10–15 minutes until the cheese is visibly bubbling at the edges.
- → Is this truly gluten-free?
Yes, all base ingredients are naturally gluten-free. Verify that butter, cheese, and any other packaged items are certified gluten-free, as some may contain hidden gluten in processing or additives.