French Onion Soup Potatoes

Last winter, after a particularly long week that felt like it would never end, I found myself alone in the kitchen with three onions and a bag of potatoes. Something about the slow, meditative process of caramelizing onions felt like exactly what I needed. The way they transformed from sharp and raw to something sweet and golden felt like a small victory in itself.

I first served this on a rainy Sunday when friends came over for what was supposed to be a casual dinner. My friend Sarah actually stopped mid conversation, put her fork down, and asked what made the onions taste so incredible. That moment of someone genuinely being wowed by something so simple stuck with me.

Ingredients

• 1.5 kg Yukon Gold or russet potatoes: I have found that Yukon Golds hold their shape beautifully while developing a creamy interior, but russets work wonderfully too. The key is slicing them exactly 1 cm thick so they cook evenly and become tender without falling apart.
• 2 tbsp olive oil: This helps the potatoes develop that gorgeous golden crust and keeps them from sticking to the parchment paper.
• ½ tsp kosher salt and ¼ tsp black pepper: Simple seasoning that lets the natural flavors shine without competing with the rich toppings.
• 3 large yellow onions: Yellow onions caramelize beautifully and become naturally sweet. I have tried red onions, but they can sometimes turn the dish a strange purple color.
• 2 tbsp unsalted butter and 1 tbsp olive oil: The combination of butter and oil prevents the butter from burning while giving the onions that incredible richness.
• ½ tsp kosher salt: This helps draw moisture out of the onions so they caramelize properly instead of steaming.
• 1 tsp fresh thyme leaves: Fresh thyme adds an earthy, aromatic quality that pairs perfectly with the sweet onions. Dried works in a pinch, but fresh really makes a difference.
• 1 tsp balsamic vinegar: My secret ingredient for adding depth and a subtle tang that balances the sweetness of the onions.
• 200 g Gruyère cheese: Gruyère melts beautifully and has that distinctive nutty flavor that makes everything taste more expensive than it actually is.
• 30 g Parmesan cheese: Optional but worth it for the salty punch and extra umami it brings to the dish.
• 2 tbsp chopped fresh parsley: Fresh parsley cuts through all the richness and adds a bright pop of color.

Instructions

Get the oven going and prep your potatoes:

Preheat your oven to 220°C and line a large baking sheet with parchment paper. Toss the potato slices with olive oil, salt, and pepper until they are evenly coated, then arrange them in a single layer on the prepared sheet.

Roast the potatoes:

Slide the potatoes into the hot oven and roast for 25 to 30 minutes. Flip them halfway through so both sides get golden and crispy. You want them tender when pierced with a fork but not falling apart.

Start the caramelized onions:

While the potatoes are roasting, heat the butter and olive oil in a large skillet over medium low heat. Add the sliced onions and salt, then cook them slowly, stirring often. This takes 25 to 30 minutes but do not rush it. The onions should turn a deep golden brown and smell incredibly sweet.

Add the finishing touches to the onions:

Stir in the fresh thyme and balsamic vinegar during the last minute or two of cooking. Let everything cook together briefly, then remove the skillet from the heat.

Assemble the dish:

Reduce your oven temperature to 200°C. Arrange the roasted potato slices in a lightly greased baking dish, slightly overlapping them like shingles. Spoon all those beautiful caramelized onions evenly over the potatoes, then sprinkle the Gruyère and Parmesan over the top.

Melt everything together:

Bake for 10 to 15 minutes until the cheese is completely melted and bubbling in spots. The edges should be starting to turn golden brown.

Serve it up:

Let the dish cool for just a few minutes so the cheese sets slightly. Scatter the fresh parsley over the top and bring it to the table while it is still steaming hot.

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This recipe has become my go to when I need to feed a crowd but want something that feels special. Watching people take that first bite, seeing their eyes light up when they hit the layer of sweet onions and salty cheese, that is what cooking is all about.

Making This Your Own

I have learned that a splash of dry white wine added to the onions during the last five minutes of cooking creates an incredibly complex flavor. The alcohol cooks off but leaves behind this subtle brightness that makes the onions taste restaurant quality. Just do not add it too early or the onions will not brown properly.

Pairing Suggestions

While this makes an incredible side dish alongside a perfectly cooked steak or roast chicken, I have also served it as a vegetarian main with a crisp green salad dressed simply with vinaigrette. The potatoes and cheese make it substantial enough that nobody misses the meat.

Make Ahead Wisdom

You can caramelize the onions up to two days in advance and keep them in the refrigerator. They actually develop even more flavor overnight. The potatoes are best roasted fresh, but you can slice them a few hours ahead and keep them submerged in cold water to prevent browning.

• Pat the potato slices completely dry with a clean kitchen towel before tossing them with oil so they roast instead of steam.
• Use the largest baking sheet you have so the potatoes have plenty of room and do not steam each other.
• Let the dish rest for at least 5 minutes after baking so the cheese sets slightly and makes serving easier.

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There is something profoundly satisfying about taking humble ingredients and transforming them into something that feels like a special occasion. This dish is proof that comfort food does not have to be complicated.

Common Questions

→ What type of potatoes work best?

Yukon Gold or russet potatoes are ideal because they hold their shape during roasting and develop a nice golden exterior. Their creamy interior texture pairs perfectly with the caramelized onions.

→ Can I prepare this dish ahead of time?

You can roast the potatoes and caramelize the onions up to a day in advance. Store them separately in the refrigerator, then assemble with cheese and bake just before serving.

→ How do I know when the onions are properly caramelized?

The onions should be deeply golden brown, almost amber in color, and very soft. This usually takes 25-30 minutes over medium-low heat. The balsamic vinegar adds a subtle sweetness and helps achieve that rich color.

→ What can I substitute for Gruyère cheese?

Swiss cheese makes an excellent substitute if Gruyère isn't available. Emmental or Comté also work well and provide similar melting properties and nutty flavor profiles.

→ Is this dish gluten-free?

Yes, this dish is naturally gluten-free as long as all your ingredients, including any packaged cheeses, are certified gluten-free. Always check labels to be certain.

→ Can I add white wine to the onions?

Absolutely. Adding a splash of dry white wine while caramelizing the onions adds depth and complexity. Deglaze the pan after the onions have browned, then let the wine cook off completely before finishing.