Caramelized Onion Soup is a comforting classic that’s all about deep, sweet onion flavor and rich, warming broth. The onions slowly cook down until they’re golden and tender, giving the soup a natural sweetness that pairs perfectly with a toasty piece of bread and melted cheese on top. It’s simple, hearty, and so satisfying.
I love making this soup when I want something that feels like a warm hug on a chilly day. The slow cooking of the onions is definitely worth the wait—there’s nothing quite like the rich aroma that fills the kitchen. My little tip? Take your time with the onions to get them perfectly caramelized; it makes all the difference in flavor.
This soup is fantastic served right out of the oven with bubbling melted cheese stretching over crusty bread. It’s one of those meals that everyone seems to enjoy, whether you’re having a casual weeknight dinner or a cozy weekend treat. I always find myself reaching for a second bowl!
Key Ingredients & Substitutions
Yellow Onions: These are the soul of the soup. Their natural sweetness deepens beautifully when caramelized. If you don’t have yellow onions, sweet onions or even red onions can work, but the flavor will differ slightly.
Butter and Olive Oil: Using both helps with flavor and browning. You can use all butter for richness or all oil for a lighter version. For dairy-free, try coconut oil or a neutral vegetable oil.
Beef Broth: This adds a rich depth, but if you prefer vegetarian, vegetable broth works great. For extra flavor, use a good quality, low-sodium broth.
White Wine: Optional but it brightens up the soup nicely. If you avoid alcohol, replace with a splash of apple cider vinegar or extra broth.
Gruyère Cheese: Classic for the melty, nutty topping. Swiss cheese is a good substitute. For a dairy-free option, try a plant-based mozzarella-style cheese, though the flavor differs.
How Do I Get Perfectly Caramelized Onions Without Burning Them?
The key is patience and medium-low heat. Start by melting butter and oil, then add sliced onions and sugar to help caramelize.
- Cook onions slowly, stirring every few minutes to avoid sticking or burning.
- If onions start to brown too fast, lower the heat. The goal is deep golden brown, soft, and sweet onions.
- This process takes 45-60 minutes — don’t rush it! The flavor develops fully only after the slow caramelization.
- Use a wide pan for better evaporation so onions don’t steam.
- Once caramelized, add garlic quickly and cook just until fragrant to avoid burning.
Equipment You’ll Need
- Large heavy-bottomed pot or Dutch oven – helps cook onions evenly without burning.
- Wooden spoon – perfect for stirring onions gently and scraping the pan.
- Chef’s knife – makes slicing onions quick and safe.
- Cutting board – sturdy surface for slicing all your ingredients.
- Oven-safe bowls or ramekins – needed for broiling cheese-topped soup safely.
- Baking sheet – holds the bowls in the oven for broiling the cheese.
Flavor Variations & Add-Ins
- Add a splash of sherry instead of white wine for a richer, slightly sweet flavor.
- Mix in caramelized mushrooms with the onions for added earthiness.
- Top with different cheeses like fontina or mozzarella for a milder, creamier melt.
- Stir in fresh herbs like rosemary or sage during simmering for a different herbal note.
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
- 2 teaspoons sugar
- 4 cloves garlic, minced
- 8 cups beef broth (or vegetable broth for vegetarian)
- ½ cup dry white wine (optional)
- 1 teaspoon fresh thyme leaves (plus extra for garnish)
- Salt and freshly ground black pepper, to taste
For the Topping:
- 1 baguette or crusty bread, sliced
- 2 cups grated Gruyère cheese (or Swiss cheese)
How Much Time Will You Need?
This recipe takes about 1 hour and 15 minutes in total. Most of that time is the slow caramelizing of the onions, which takes about 45 to 60 minutes. After that, simmering the soup and preparing the bread and cheese topping will take another 15-20 minutes.
Step-by-Step Instructions:
1. Caramelize the Onions:
In a large heavy-bottomed pot or Dutch oven, melt the butter with olive oil over medium heat. Add the sliced onions and sprinkle the sugar over them to help caramelize. Stir occasionally and cook slowly for about 45 to 60 minutes, until the onions are deeply golden and soft. If they start browning too fast, lower the heat to avoid burning.
2. Build the Soup Base:
Add the minced garlic to the onions and cook for another minute until fragrant. Pour in the white wine (if you’re using it) to deglaze the pan, scraping up any flavorful bits stuck to the bottom. Let the wine cook down for about 2-3 minutes.
Then, add the beef broth and thyme leaves. Bring the soup to a simmer and let it cook gently for 20-30 minutes to let the flavors blend. Season with salt and pepper to your taste.
3. Prepare and Broil the Topping:
While the soup simmers, preheat your oven’s broiler. Arrange the sliced bread on a baking sheet and toast lightly on both sides in the oven or toaster. When ready to serve, ladle the hot soup into oven-safe bowls. Place one or two toasted bread slices on top of each bowl of soup, then generously sprinkle grated Gruyère cheese over the bread.
Place the bowls back on the baking sheet and broil in the oven until the cheese melts, bubbles, and turns golden, about 3-5 minutes. Keep an eye on them so they don’t burn!
4. Serve:
Carefully remove the bowls from the oven, garnish each serving with fresh thyme, and enjoy your comforting bowl of caramelized onion soup!
Can I Use Frozen Onions for This Soup?
It’s best to use fresh onions since caramelizing relies on their moisture content and texture. If you must use frozen, thaw completely and drain any excess water before cooking to avoid soggy onions.
Can I Make Caramelized Onion Soup Ahead of Time?
Absolutely! You can prepare the soup up to the simmering step, then cool and refrigerate for up to 3 days. Reheat gently on the stove before adding bread and cheese toppings to broil.
How Should I Store Leftovers?
Store any leftover soup in an airtight container in the refrigerator for up to 3 days. Keep the bread and cheese separate to prevent sogginess. Reheat the soup and add fresh toasted bread and cheese before serving.
What Can I Substitute for Gruyère Cheese?
Swiss cheese is a great substitute for Gruyère and melts well. If you want a milder flavor, mozzarella or fontina also work nicely. For a non-dairy option, try plant-based cheese that melts well, though the flavor will differ.
