Caramelized Onion Soup is a warm and comforting bowl full of rich, sweet onions slowly cooked until golden brown and tender. The deep flavor of the onions blended with a savory broth creates a simple yet satisfying dish that feels like a cozy hug in a bowl.
I love making this soup when I want something that fills the house with the smell of home. Taking the time to caramelize the onions patiently really makes all the difference—it brings out their natural sweetness that balances perfectly with a touch of salt and herbs. I usually stir gently and enjoy how the onions transform right before my eyes.
My favorite way to enjoy this soup is with a slice of toasted bread topped with melted cheese floating on top. It makes every spoonful extra special and comforting, especially on a chilly day. It’s one of those easy recipes that always makes everyone smile and feel a little more at ease.
Key Ingredients & Substitutions
Yellow Onions: These are the best choice for caramelizing because they develop a natural sweetness. If you don’t have yellow onions, sweet onions or even white onions will work but the flavor will be slightly different.
Butter & Olive Oil: Using both helps caramelize onions without burning. Butter adds richness while olive oil raises the smoke point. You can use all olive oil if preferred for a dairy-free option.
Broth: Beef broth gives a deeper flavor, but vegetable broth is great for a lighter or vegetarian soup. You can even mix both to keep the depth but lighten the dish.
Gruyère Cheese: This cheese melts beautifully and has a nice nuttiness perfect for topping the soup. Swiss cheese is a good substitute. For a sharper flavor, Fontina or Emmental work too.
Bread: A crusty baguette holds up well when toasted and placed on the soup. If you don’t have baguette, any sturdy crusty bread will work. Just toast it well to avoid sogginess.
How Do You Get Perfectly Caramelized Onions Without Burning Them?
Caramelizing onions is key to the soup’s flavor, but it takes patience. Here’s how to do it well:
- Cook onions slowly over medium to medium-low heat to allow their natural sugars to develop without burning.
- Stir occasionally, but not constantly—this helps them brown evenly and stick to the pan a little to build flavor.
- Add a little sugar after 10 minutes to speed up caramelization and deepen sweetness.
- If onions start sticking too much, add a splash of water to loosen the bits and avoid burning.
- It should take about 25-30 minutes for onions to turn a deep golden brown, soft, and flavorful.
Taking your time here creates the rich, slightly sweet base needed for a great caramelized onion soup.
Equipment You’ll Need
- Large heavy-bottomed pot or Dutch oven – helps cook the onions evenly without burning them.
- Wooden spoon or heatproof spatula – perfect for stirring the onions gently while caramelizing.
- Chef’s knife – sharp for slicing onions thinly and evenly.
- Baking sheet – to toast the bread slices before topping with cheese.
- Oven-safe soup bowls or ramekins – so you can broil the soup and melt the cheese right in the bowl.
Flavor Variations & Add-Ins
- Add a splash of sherry or brandy instead of white wine for a richer, deeper flavor.
- Replace thyme with rosemary or sage for an earthier herb note that pairs well with the sweet onions.
- Mix in cooked mushrooms along with onions for a heartier texture and umami boost.
- Top with a blend of cheeses like mozzarella and Parmesan for extra gooeyness and sharpness.
How to Make Caramelized Onion Soup?
Ingredients You’ll Need:
For the Soup:
- 4 large yellow onions, thinly sliced
- 3 tablespoons unsalted butter
- 1 tablespoon olive oil
- 1 teaspoon granulated sugar
- 2 cloves garlic, minced
- 1/4 cup dry white wine (optional)
- 6 cups beef or vegetable broth
- 1 teaspoon fresh thyme leaves (or 1/2 teaspoon dried thyme)
- 1 bay leaf
- Salt and freshly ground black pepper, to taste
For the Topping:
- Baguette or crusty bread, sliced
- 1 1/2 cups grated Gruyère or Swiss cheese
- Fresh thyme sprigs, for garnish (optional)
How Much Time Will You Need?
This recipe takes about 10 minutes of prep time and around 1 to 1.5 hours of cooking, mainly due to the slow caramelization of the onions. You’ll also spend a few minutes toasting the bread and melting the cheese at the end. Patience while caramelizing the onions really pays off with deep flavor!
Step-by-Step Instructions:
1. Caramelizing the Onions:
In a large pot over medium heat, melt the butter together with the olive oil. Add the thinly sliced onions and stir them well to coat in the butter and oil. Cook the onions slowly, stirring occasionally, for about 25-30 minutes until they turn a lovely deep golden brown and taste sweet. About 10 minutes into cooking, sprinkle the sugar over the onions to help the caramelization process along.
2. Adding Garlic and Deglazing:
Once the onions are caramelized, add the minced garlic and cook for another minute until the aroma fills your kitchen. Pour in the white wine if you’re using it, and let it simmer gently until most of the liquid evaporates, scraping the bottom of the pot to get all those tasty browned bits.
3. Making the Soup Base:
Add the broth, fresh or dried thyme, and the bay leaf to the pot. Bring the soup to a gentle simmer and let it cook for 20-30 minutes to let the flavors come together. Taste and season with salt and pepper as you like.
4. Preparing the Bread and Cheese Topping:
While the soup is simmering, preheat your oven’s broiler. Arrange the sliced baguette or crusty bread on a baking sheet and toast until golden on both sides. When ready to serve, ladle the hot soup into oven-safe bowls, place one or two toasted bread slices on top, and generously sprinkle with grated Gruyère or Swiss cheese.
5. Broiling to Perfection:
Put the bowls under the broiler for 3-5 minutes until the cheese is melted, bubbly, and nicely browned. Keep a close eye so the cheese doesn’t burn. Carefully remove the bowls (they’ll be hot!), garnish with fresh thyme if you want, and enjoy your comforting bowl of caramelized onion soup!
Can I Use Frozen Onions for This Soup?
It’s best to use fresh onions for caramelized onion soup because frozen ones release more water and can make the soup watery. If you must use frozen, thaw completely and pat dry before cooking to reduce excess moisture.
How Can I Make This Soup Vegetarian or Vegan?
Use vegetable broth instead of beef broth for a vegetarian version. For vegan, also replace butter with olive oil and choose a dairy-free cheese or skip the cheese topping altogether.
Can I Prepare This Soup Ahead of Time?
Yes! You can caramelize the onions and make the soup base up to 2 days ahead. Store the soup in the fridge and reheat gently before adding bread and cheese toppings and broiling just before serving.
What’s the Best Way to Store Leftovers?
Keep leftover soup in an airtight container in the refrigerator for up to 3 days. Reheat on the stove over medium-low heat and add a splash of broth if it’s too thick. Add fresh toasted bread and cheese when serving again.
