Caramelized Onion Soup is a warm and comforting dish that shines with the deep sweetness of slowly cooked onions. This soup brings together rich, golden caramelized onions and a flavorful broth that feels cozy with every spoonful. It’s a simple dish with a classic taste that feels like a little hug in a bowl.
I love making this soup when I want something soothing but special. Taking the time to caramelize the onions until they’re soft and golden really makes all the difference—it’s worth the wait! I usually stir in a splash of wine or a sprinkle of thyme to give it a touch of warmth and extra depth.
My favorite way to serve this soup is with a toasted slice of crusty bread on top, melted cheese included if I’m feeling fancy. It’s perfect for chilly evenings or when I need something easy to bring the family together around the dinner table. Plus, it’s such a great way to turn humble onions into a meal that everyone loves!
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Key Ingredients & Substitutions
Yellow Onions: These are great for caramelizing because of their natural sweetness. If you don’t have yellow onions, sweet onions or even Vidalia work well. Avoid red onions here since they’re sharper.
Butter & Olive Oil: Using both helps with flavor and prevents burning. You can swap butter for all olive oil if dairy-free, but butter adds richness I love.
Broth: Beef broth gives a deep, hearty flavor, but vegetable broth is perfect if you prefer a lighter or vegetarian soup.
Gruyère Cheese: It melts beautifully and adds nutty flavor. Swiss cheese or mozzarella can work if Gruyère isn’t available, though they have milder taste.
How Do You Perfectly Caramelize Onions Without Burning Them?
Caramelizing onions takes patience, but it’s key to the soup’s flavor. Here are my steps:
- Heat butter and olive oil on medium-low heat.
- Add sliced onions with salt and sugar. Stir often to avoid sticking or burning.
- Cook slowly for 40-50 minutes until they turn golden brown and soft.
- Adjust heat if onions start to burn—lower it to keep a gentle sizzle.
- Stir frequently, scraping the pan bottom to loosen browned bits for deeper flavor.
This slow process brings out the onions’ natural sweetness and adds rich color and depth to your soup.
Equipment You’ll Need
- Heavy-bottomed pot – holds heat evenly to slowly caramelize onions without burning.
- Wooden spoon – perfect for stirring onions gently and scraping browned bits off the bottom.
- Chef’s knife – sharp and sturdy for slicing onions thinly and safely.
- Oven-safe soup bowls or crocks – to broil the cheese-topped soup right in the serving dish.
- Broiler or oven – for melting and browning the cheese topping beautifully.
Flavor Variations & Add-Ins
- Swap the Gruyère with sharp cheddar for a tangier, mellow twist.
- Add a splash of sherry or brandy with the wine to deepen richness and warmth.
- Stir in sautéed mushrooms or roasted garlic for extra earthy notes and texture.
- Use caramelized leeks instead of onions for a milder, sweeter flavor variation.
How to Make Caramelized Onion Soup?
Ingredients You’ll Need:
- 4 large yellow onions, thinly sliced
- 3 tablespoons unsalted butter
- 1 tablespoon olive oil
- 1 teaspoon salt
- ½ teaspoon sugar
- 3 cloves garlic, minced
- ¼ cup dry white wine (optional)
- 6 cups beef or vegetable broth
- 2 sprigs fresh thyme
- 1 bay leaf
- Freshly ground black pepper, to taste
- Baguette or crusty bread, sliced
- 1 ½ cups grated Gruyère or Swiss cheese
How Much Time Will You Need?
This recipe takes about 1 hour and 30 minutes total. Preparing and caramelizing the onions takes about 40–50 minutes, and then simmering the soup for good flavor takes another 30 minutes. Toasting the bread and melting the cheese under the broiler will only take a few minutes more. Patience while caramelizing the onions is key to delicious results!
Step-by-Step Instructions:
1. Caramelize the Onions:
Heat the butter and olive oil in a large heavy-bottomed pot over medium heat. Add the sliced onions, salt, and sugar. Cook, stirring often, for about 40 to 50 minutes until the onions are soft, golden, and deeply caramelized. Adjust the heat to make sure they don’t burn.
2. Add Garlic and Wine:
Stir in the minced garlic and cook for another 1-2 minutes until it smells wonderful. Pour in the white wine, if using, and cook until mostly evaporated, gently scraping up browned bits from the pot’s bottom for extra flavor.
3. Simmer the Soup:
Add the broth, thyme sprigs, and bay leaf. Bring everything to a boil, then lower the heat and simmer uncovered for 30 minutes. This lets all the flavors come together nicely. Remove the thyme and bay leaf, then taste and adjust salt and pepper.
4. Prepare Bread and Cheese Topping:
Preheat your oven’s broiler. Arrange the baguette slices on a baking sheet and toast them until golden. Then ladle the hot soup into oven-safe bowls. Place a toasted baguette slice or two on top of each bowl, and sprinkle generously with grated Gruyère or Swiss cheese.
5. Broil and Serve:
Put the bowls under the broiler and cook just until the cheese melts and turns bubbly and golden, about 2-4 minutes. Keep a close eye on them to avoid burning. Garnish with fresh thyme leaves if you like, and serve immediately for a warm, cozy meal!
Can I Use Frozen Onions for This Soup?
It’s best to use fresh onions for caramelizing because frozen onions tend to release extra moisture, making it harder to get that rich golden color. If you must use frozen, thaw and drain them well before cooking, then cook low and slow to help evaporate moisture.
Can I Make This Soup Ahead of Time?
Yes! The soup actually tastes better the next day as the flavors meld. Cool completely, then refrigerate in an airtight container for up to 3 days. Reheat gently on the stove and add a bit of broth if it’s too thick before broiling the cheese and bread topping.
What Can I Substitute for Gruyère Cheese?
Gruyère has a lovely nutty flavor, but Swiss cheese or mozzarella are good milder substitutes. Cheddar can also work for a sharper taste. Just be sure to use a cheese that melts well so you get that bubbly, gooey topping.
How Do I Store Leftovers?
Store leftover soup in airtight containers in the fridge for up to 3 days. Keep bread and cheese toppings separate until ready to serve to prevent sogginess. Reheat the soup on the stove and broil bread and cheese fresh for best texture.
