Caramelized Onion Soup is a cozy bowl of deep, sweet onion flavor made by slowly cooking onions until they’re soft, golden, and rich. This soup has a beautiful balance of sweetness from the caramelized onions and a warm, savory broth that feels like a gentle hug on a chilly day.
I love making this soup on weekends when I have a little extra time to let those onions cook low and slow. The smell that fills the kitchen as they caramelize is honestly one of the best parts—it’s like the whole house is inviting you to settle in and relax. A tip I swear by is stirring often and being patient, because good things really do take time with this soup.
When I serve Caramelized Onion Soup, I like to top it with melty cheese and some crusty bread right on top, then pop it under the broiler for a few minutes. It turns into this wonderful gooey, toasty treat that everyone always asks for seconds of. It’s the kind of dish that’s perfect for winding down and sharing with friends or family on a quiet evening.
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Key Ingredients & Substitutions
Yellow Onions: These are best for caramelizing because they become naturally sweet and soft. If you can’t find yellow onions, white onions work but are a bit sharper in taste.
Butter and Olive Oil: Using both adds richness and helps with even cooking. You can swap butter for all olive oil for a dairy-free version.
Broth: Beef broth gives a deep, meaty flavor. For vegetarians, vegetable broth keeps the soup light but tasty.
Cheese: Gruyère melts beautifully and adds nuttiness. Swiss cheese is a good substitute. For a milder option, try mozzarella or provolone.
Bread: Crusty baguette slices toast well and hold up under the cheese. Any firm bread like ciabatta also works.
How Do You Get Perfectly Caramelized Onions Without Burning Them?
Caramelizing onions takes time, but the results are worth it. Here’s how to do it step-by-step:
- Use a wide, heavy-bottomed pan to cook the onions evenly.
- Cook over medium-low heat so they soften without burning.
- Stir often—about every 5 minutes to prevent sticking and burning.
- Be patient! This step takes 40–50 minutes, and the onions will slowly turn golden brown and sweet.
- Adding a small pinch of sugar halfway helps speed up the caramelization without burning.
If the onions start to stick or dry out, add a splash of water or broth to loosen the pan bits and keep cooking.
Equipment You’ll Need
- Large heavy-bottomed pot – it helps caramelize the onions evenly without burning.
- Wooden spoon – perfect for stirring often and scraping up browned bits gently.
- Sharp knife and cutting board – to slice onions thinly and safely.
- Oven-safe bowls or crocks – so you can broil the cheese on top of the soup.
- Baking sheet – to toast the bread slices evenly under the broiler.
Flavor Variations & Add-Ins
- Swap beef broth for mushroom broth to keep it vegetarian with a rich, earthy flavor.
- Add a splash of sherry or brandy instead of white wine for a deeper, slightly sweet taste.
- Try topping the soup with Swiss or mozzarella cheese if you want a milder, creamier melt.
- Mix in sautéed mushrooms or fresh thyme for extra earthy aroma and a herbal touch.
Caramelized Onion Soup
Ingredients You’ll Need:
Main Ingredients:
- 4 large yellow onions, thinly sliced
- 3 tablespoons unsalted butter
- 2 tablespoons olive oil
- 1 teaspoon sugar
- 2 cloves garlic, minced
- ½ cup dry white wine (optional)
- 6 cups beef broth (or vegetable broth for a vegetarian option)
- 2 sprigs fresh thyme
- 1 bay leaf
- Salt and freshly ground black pepper, to taste
Toppings:
- 1 baguette or crusty bread, sliced
- 2 cups grated Gruyère cheese (or Swiss cheese)
How Much Time Will You Need?
This soup takes about 15 minutes to prepare the onions and ingredients, 40-50 minutes to caramelize the onions slowly, plus 30 minutes simmering to develop the flavors. Toasting the bread and broiling with cheese will take about 10 minutes. Expect around 1 hour 30 minutes total, including cooking and finishing steps.
Step-by-Step Instructions:
1. Caramelizing the Onions:
Heat butter and olive oil in a large pot over medium heat until melted and shimmering. Add the thinly sliced onions and coat them well. Turn the heat to medium-low and cook the onions slowly, stirring frequently. After about 20 minutes, sprinkle sugar to help caramelize. Continue cooking for a total of 40-50 minutes until onions are golden brown and sweet.
2. Building the Soup Base:
Add minced garlic to the pot and cook for 1 minute. Pour in the white wine if using, scraping any browned bits off the pot’s bottom. Let it reduce for a few minutes. Add the broth, thyme, and bay leaf. Bring to a simmer, cook gently for 30 minutes, and season with salt and pepper.
3. Preparing the Toppings and Serving:
Preheat your oven’s broiler. Toast the bread slices on a baking sheet until golden on both sides. Ladle the soup into oven-safe bowls, place a toasted bread slice on top, and sprinkle with grated cheese. Place bowls under the broiler just until cheese melts and bubbles. Garnish with fresh thyme and serve immediately.
Can I Use Frozen Onions for This Soup?
It’s best to use fresh onions for caramelizing since frozen ones tend to release extra moisture and won’t brown properly. If you only have frozen, thaw and drain them thoroughly before cooking, but fresh is always ideal.
Can I Make Caramelized Onion Soup in Advance?
Absolutely! You can prepare the soup up to the simmering step, then cool and refrigerate it for up to 3 days. When ready to serve, reheat gently, add the bread and cheese topping, and broil as usual.
What Cheese Can I Substitute for Gruyère?
If you don’t have Gruyère, Swiss cheese is a great substitute. Mozzarella or provolone can also work for a milder taste, but Gruyère’s nutty flavor is perfect if you can find it.
How Should I Store Leftover Soup?
Store any leftover soup in an airtight container in the fridge for up to 3 days. Reheat it on the stove over medium heat, stirring occasionally. Add fresh bread and cheese before serving again.
