This creamy caramelized onion and fennel soup is a comforting plant-based delight that’s naturally gluten-free and vegan.
Packed with fiber, plant-based protein from cashews, and heart-healthy fats, it’s nourishing and light at the same time.
With simple ingredients and minimal prep, it’s an ideal everyday soup—perfect for a quick weeknight dinner or make-ahead meal prep.
Caramelized Onion Soup
Equipment
- 1 large saucepan or soup pot
- 1 blender (or immersion blender)
- 1 Cutting board
- 1 Chef’s knife
- Measuring Spoons and Cups
Ingredients
- 3 tablespoons olive oil
- 5 medium yellow onions peeled and sliced
- 3 tablespoons raw apple cider vinegar
- 1 large fennel bulb trimmed and chopped
- 5 cups filtered water
- 1 teaspoon fresh rosemary chopped
- 1 bay leaf
- ½ cup raw cashews
- 1 teaspoon fine sea salt
- ¼ teaspoon black pepper
Instructions
- Prepare the Onions: Begin by peeling and thinly slicing all five yellow onions. Take your time to cut them evenly, as uniform slices help ensure consistent caramelization. Place a large, heavy-bottomed saucepan over medium heat and add three tablespoons of olive oil. Once the oil shimmers but doesn’t smoke, gently add the sliced onions. Stir frequently, letting them soften and turn translucent, which should take about 10 minutes. This stage releases their natural sweetness, forming the flavor foundation of the soup.
- Enhance the Caramelization: After the onions are soft, raise the heat to medium-high for one minute, stirring continuously. This quick increase in heat encourages gentle browning on the edges. Next, pour in three tablespoons of raw apple cider vinegar. Stir thoroughly, scraping the bottom of the pan with a wooden spoon to lift any caramelized bits. This step intensifies the depth of flavor and adds a subtle tang that balances the natural sweetness.
- Prepare and Add Fennel: While the onions cook, trim the fennel bulb by cutting off the stalks and tough outer layers, then chop it into small, bite-sized pieces. Reduce the heat to medium-low and add the chopped fennel to the onions. Continue cooking for approximately 20 minutes, stirring occasionally. Allow both the onions and fennel to slowly caramelize. The vegetables should become golden brown and fragrant, releasing a sweet, slightly licorice-like aroma that signals readiness.
- Introduce Aromatics and Liquids: Once the onions and fennel are beautifully caramelized, pour in five cups of filtered water. Add one teaspoon of chopped fresh rosemary and a whole bay leaf. These aromatics elevate the soup with herbal undertones. Stir to combine, then add 1/2 cup of raw cashews, one teaspoon of fine sea salt, and 1/4 teaspoon of freshly ground black pepper. Let the soup simmer gently for five minutes, allowing the cashews to soften and the flavors to meld together.
- Blend to Creamy Perfection: After simmering, remove the bay leaf from the soup. Transfer the mixture to a blender, or use an immersion blender directly in the pot. Blend until the soup reaches a smooth, velvety consistency. If needed, add a splash of water to adjust thickness. Taste and adjust seasoning with additional salt or pepper if desired. The result should be a luxuriously creamy, naturally sweet, and savory soup with no dairy required.
- Serve and Enjoy: Ladle the soup into warm bowls and optionally garnish with a small sprig of rosemary, a drizzle of olive oil, or freshly cracked black pepper.Serve immediately for a comforting meal, or let it cool slightly and store in airtight containers for meal prep. This soup pairs wonderfully with crusty bread or a light green salad, making it perfect for a satisfying, nutrient-packed dinner or lunch.
Notes
- Use yellow onions for natural sweetness; red onions will alter flavor and color.
- For a smoother texture, soak raw cashews in warm water for 15–20 minutes before blending.
- Stir frequently while caramelizing to prevent burning and promote even browning.
- Adjust seasoning after blending; blending can mellow flavors, so taste before serving.
- For a richer flavor, roast fennel in the oven for 10 minutes before adding.
- Gluten-free and vegan as written; optionally top with croutons or a swirl of plant-based cream.
- Soup thickness can be adjusted with extra water or vegetable broth.
Chef’s Secrets To Maximum Flavor
The secret to this soup’s deeply rich and complex flavor is patience.
Caramelizing the onions and fennel slowly allows natural sugars to develop and creates layers of sweetness that balance the tang of apple cider vinegar.
Using raw cashews instead of cream adds both protein and healthy fats while keeping the soup vegan.
Fresh rosemary provides a subtle herbal aroma, but adding it toward the end of cooking ensures it doesn’t overpower the soup.
Always scrape the pan while sautéing to incorporate the flavorful browned bits at the bottom, which intensifies the overall taste.
Serving Suggestions For Perfect Meals
This caramelized onion and fennel soup is versatile and pairs beautifully with many accompaniments.
Serve it with warm, crusty bread or lightly toasted baguette slices for a classic combination.
A side salad of mixed greens, arugula, or baby spinach dressed with lemon vinaigrette complements the soup’s sweetness.
For heartier options, add roasted chickpeas or a sprinkle of toasted seeds on top for texture and extra protein.
Drizzling a small amount of olive oil or adding fresh herbs like thyme or parsley before serving elevates both presentation and flavor.
Storage Tips For Fresh Soup
Store this soup in an airtight container in the refrigerator for up to 4–5 days.
For longer storage, pour into freezer-safe containers and freeze for up to 3 months.
To reheat, gently warm on the stovetop over low heat, adding a splash of water if it has thickened during storage.
Avoid boiling to preserve the creamy texture.
Leftover soup can also be repurposed as a base for sauces, grain bowls, or casseroles, making it convenient for meal prep and reducing food waste.
Frequently Asked Questions
1. Can I use other types of onions?
Yes, you can substitute yellow onions with white onions, but red onions may alter the color and add a sharper, less sweet flavor. Yellow onions provide the perfect balance of sweetness and body for caramelization.
2. Do I have to use cashews for creaminess?
Cashews give a rich, silky texture without dairy, but you can use soaked almonds, sunflower seeds, or even canned coconut milk as alternatives. Blending thoroughly is key to achieving a smooth consistency.
3. Can I make this soup ahead of time?
Absolutely! This soup tastes even better the next day as the flavors deepen. Store in an airtight container in the fridge for up to 5 days or freeze in portions for convenience.
4. How can I adjust the thickness?
If the soup is too thick, add water or unsalted vegetable broth gradually while blending. For a thicker version, reduce the amount of liquid or cook longer to concentrate flavors.
5. Is this soup suitable for low-sodium diets?
Yes, it can easily be adjusted. Simply reduce the added salt and use filtered water. The natural sweetness from the caramelized vegetables ensures it remains flavorful even with less sodium.
