Caramelized Onion Soup is a rich, comforting bowl full of sweet, slow-cooked onions and warm, savory broth. The onions melt into a golden, silky base that fills the kitchen with the most inviting aroma. This soup is simple but feels special with every spoonful thanks to the deep, natural flavors that develop during caramelization.
I love making this soup when I want something cozy and satisfying without a lot of fuss. Taking the time to slowly cook the onions until they’re soft and sweet is worth every minute—it’s like building layers of flavor that make the soup taste like it’s been simmering all day. A little tip I like to share is to stir often and be patient; it makes all the difference in getting those perfect golden-brown onions.
Serving this soup with a crusty piece of bread or topped with melted cheese is my favorite way to enjoy it. It’s the kind of meal that feels like a warm hug, especially on a chilly day. Whenever I make caramelized onion soup, it’s always a hit, and I find myself looking forward to the leftovers just as much as the fresh batch.
Key Ingredients & Substitutions
Yellow Onions: These are perfect for caramelizing thanks to their natural sweetness. If you can’t find yellow onions, sweet onions like Vidalia work well too.
Butter & Olive Oil: Using both adds richness and helps prevent burning. You can swap butter for all olive oil if you want a dairy-free version.
Beef Broth: It gives the soup a deep, meaty flavor. For a lighter or vegetarian option, use vegetable broth, but the flavor will be milder.
Gruyère Cheese: This cheese melts beautifully and has a nutty taste. Swiss or mozzarella can be good alternatives if Gruyère isn’t available.
Bread: A crusty baguette adds great texture. Any sturdy bread like sourdough or ciabatta will work for toasting.
How Do You Perfectly Caramelize Onions Without Burning Them?
Caramelizing onions takes time and patience, but it’s key for that deep sweet flavor.
- Use a heavy-bottomed pan to distribute heat evenly.
- Cook onions slowly over medium or medium-low heat.
- Stir frequently—every few minutes—to prevent sticking and burning.
- Add a pinch of sugar to boost caramelization.
- If onions start browning too fast, lower the heat and add a splash of water to loosen bits from the pan.
- Expect this to take 40-50 minutes for rich, golden onions.
Equipment You’ll Need
- Large heavy-bottomed pot or Dutch oven – perfect for even heat and slow caramelizing without burning the onions.
- Wooden spoon or silicone spatula – lets you stir frequently and scrape the pan easily without damaging cookware.
- Whisk – helps mix the flour smoothly into the onions to avoid lumps.
- Oven-safe soup bowls or crocks – needed to broil the cheese-topped soup safely.
- Baking sheet – to hold the bowls under the broiler, catching any drips.
Flavor Variations & Add-Ins
- Add a splash of dry sherry or brandy before simmering for a deeper, slightly sweet flavor twist.
- Stir in cooked mushrooms or caramelized shallots for extra earthiness and texture.
- Top with different cheeses like fontina or sharp cheddar for a melty but different cheesy experience.
- Include fresh herbs like rosemary or sage with thyme to give a more complex herbal aroma.
Caramelized Onion Soup
Ingredients You’ll Need:
For the Soup:
- 6 large yellow onions, thinly sliced
- 4 tablespoons unsalted butter
- 1 tablespoon olive oil
- 2 cloves garlic, minced
- 1 teaspoon sugar
- ½ teaspoon salt
- ¼ teaspoon black pepper
- 2 tablespoons all-purpose flour
- 8 cups beef broth (or a mix of beef and chicken broth)
- ½ cup dry white wine or dry sherry (optional)
- 1 tablespoon Worcestershire sauce (optional)
- 1 teaspoon fresh thyme leaves, plus extra for garnish
- 1 bay leaf
For Serving:
- Baguette or crusty French bread, sliced
- 2 cups grated Gruyère cheese (or Swiss cheese)
How Much Time Will You Need?
Plan for about 1 hour and 30 minutes total, including 50 minutes to slowly caramelize the onions and another 30 minutes simmering the soup. Toasting the bread and broiling the cheese-topped bowls will take about 10–15 minutes.
Step-by-Step Instructions:
1. Caramelize the Onions:
In a large heavy-bottomed pot or Dutch oven, heat butter and olive oil over medium heat until melted. Add the sliced onions, sugar, salt, and pepper. Cook, stirring frequently, for about 40–50 minutes until the onions become soft, deeply golden, and caramelized. Adjust heat as needed to prevent burning, and be patient—this slow cooking develops the soup’s rich flavor.
2. Build the Soup:
Add the minced garlic to the onions and cook for 1 more minute until fragrant. Sprinkle the flour over the onions and stir constantly for 2–3 minutes to cook out the raw flour taste. Gradually pour in the broth while stirring, scraping up any browned bits on the pot’s bottom. Add the wine or sherry (if using), Worcestershire sauce, fresh thyme, and bay leaf. Bring to a boil, then reduce heat to low and simmer gently for 30 minutes. Taste and adjust seasoning with salt and pepper as needed.
3. Prepare and Serve:
Preheat your broiler. While the soup simmers, toast slices of baguette or crusty bread until golden and crisp. Ladle the hot soup into oven-safe bowls, place toasted bread slices on top, then sprinkle generously with grated Gruyère cheese. Place the bowls on a baking sheet and broil for 3–5 minutes until the cheese is bubbly, melted, and browned in spots—watch carefully to avoid burning. Remove from the oven, garnish with fresh thyme sprigs, and serve immediately for a warm and comforting meal.
Can I Use Frozen Onions for This Soup?
It’s best to use fresh onions because frozen ones can release excess water, making caramelization harder. If you only have frozen onions, thaw and drain them well before cooking to reduce moisture.
Can I Make Caramelized Onion Soup Ahead of Time?
Yes! You can caramelize the onions and prepare the soup base up to 2 days in advance. Store it in the fridge and reheat gently on the stove before adding the bread and cheese topping.
What Can I Use Instead of Gruyère Cheese?
If you can’t find Gruyère, Swiss cheese or mozzarella make good substitutes. They melt nicely and provide a mild, nutty flavor similar to Gruyère.
How Should I Store Leftovers?
Keep leftover soup in an airtight container in the refrigerator for up to 3 days. Reheat it on the stove gently and add fresh toasted bread and cheese when serving to maintain the best texture.
