A silky, creamy soup featuring caramelized onions and fennel, lightly seasoned with rosemary. Cashews add a subtle richness and plant-based protein, making it a nourishing, low-fat, gluten-free, and vegan option perfect for cozy weeknights or meal prep.
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.