Cauliflower Fennel Soup

This cauliflower fennel soup is silky, creamy and full of gentle, sweet flavor, and it's easy to make with just a handful of ingredients. Roasting the vegetables first gives it a toasty depth, and a side of crunchy garlic "crostini" turns a bowl of it into a proper low carb lunch.

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Fennel is usually paired with potatoes, leeks, apples or beans in soup, none of which are particularly low carb. Cauliflower turns out to be the perfect partner instead: it blends up just as smooth and creamy as potato, and it lets the fennel's flavor shine. The result is a simple soup with a lot of flavor.

Key Ingredients & Substitutions

• Fennel. The star of the show. Raw fennel has a fresh, licorice-like crunch, but roasting mellows it into something sweet, nutty and much more subtle, so even people who don't love anise tend to enjoy this soup. It adds natural sweetness and a lovely aromatic note that keeps the cauliflower from tasting flat. Look for a firm, white bulb with bright green fronds, and save a few fronds for the garnish. If you'd like a stronger fennel flavor, add a pinch of fennel seeds to the vegetables before roasting. Want more ideas for using it? Try this Roasted Creamy Fennel side dish.
• Cauliflower. The low carb stand-in for potato. It gives the soup body and a velvety texture once it's blended. Fresh florets roast best, but frozen florets work too; roast them straight from frozen and add a few extra minutes.
• Olive oil. Helps the vegetables brown and adds richness. Avocado oil or melted butter are good swaps. Here's my guide to olive oil for low carbers if you want to pick a good one.
• Broth. Use vegetable broth to keep it vegetarian, or chicken broth for a deeper, more savory soup. I love Kettle and Fire chicken bone broth, which adds extra protein and body. Read more about the low carb benefits of bone broth.
• Heavy cream. Just a quarter cup makes the soup rich and smooth. For a dairy-free version, use full-fat coconut milk instead; it adds a faint coconut note that goes surprisingly well with fennel.
• Low carb bagel chips. The base for the garlic "crostini." They're already crunchy, so they just need a quick trip under the broiler with garlic herb butter. I've used keto bagel chips, but slices of low carb bread or homemade cheese crisps work too. Note that most bagel chips are not gluten free.

Helpful Tips

Cut the vegetables to a similar size. Chop the fennel bulb into pieces about the same size as the cauliflower florets so everything roasts evenly. Trim off the tough stalks and the root end first, but keep the feathery fronds for garnish.

Don't skip the browning. Those golden, caramelized edges are where the flavor comes from. Spread the vegetables in a single layer with a little space between them, and roast until the edges turn brown rather than pulling them out as soon as they soften.

Blend safely. Let the roasted vegetables cool for a few minutes before they go into the blender, and vent the lid (or cover the opening with a folded towel) so steam can escape. A high-speed blender like the Ninja Professional gives the smoothest texture, but an immersion blender in the saucepan works fine too.

Adjust the thickness. If the soup is thicker than you like, add a splash more broth while it heats. If it's too thin, simmer it uncovered for a few minutes to reduce it, but keep the heat gentle once the cream is in so it doesn't boil.

Season at the end. Broths vary a lot in saltiness, so taste the soup after the cream goes in and add salt and pepper then. A little squeeze of lemon juice right before serving brightens the flavor too.

Variations

• Cheesy. Stir in a handful of grated Parmesan or Gruyere along with the cream for a richer, savory soup.
• Bacon-topped. Crumble crispy bacon over each bowl for a salty, smoky crunch.
• Garlic and onion. Roast a few whole garlic cloves and a wedge of onion with the vegetables for a deeper, sweeter base.
• Lemon and herb. Finish with lemon zest and fresh dill or parsley for a lighter, spring-style soup.
• Spiced. Add a pinch of smoked paprika or cumin before roasting for gentle warmth.
• Dairy-free. Swap the cream for coconut milk and the butter on the crostini for olive oil.

Serving Ideas

The garlic crostini are the classic pairing here. Spread the bagel chips with garlic herb butter and slide them under the broiler for a minute or two while you ladle out the soup. They're crunchy, buttery and perfect for dunking. If you like the idea, these Low Carb Crostini with Cranberries & Herbed Cheese make a fun party version.

To make it a fuller meal, serve the soup with a crisp side salad, such as this Low Carb Fennel Salad, or with grilled chicken, a piece of salmon or a cheesy omelet. A full bowl (about 2 cups) makes a satisfying lunch on its own, while a smaller cup is a lovely starter for a holiday dinner.

Storing & Freezing

Let the soup cool, then store it in an airtight container in the fridge for up to 4 days. It thickens a little as it chills, so add a splash of broth or water when you reheat it gently on the stove or in the microwave. Keep the crostini separate in an airtight container at room temperature so they stay crunchy, and add the garlic butter just before serving.

The soup freezes well for up to 3 months. For the best texture, freeze it before adding the cream: thaw it overnight in the fridge, warm it through on the stove, then stir in the cream. If you've already added the cream, it may separate slightly after thawing; a quick whisk or a few seconds with an immersion blender brings it back together.

More Low Carb Soups and Fennel Recipes

If you loved this soup, here are a few more you might enjoy:

• Low Carb Purple Cauliflower Soup
• Low Carb Broccoli Cheese Soup
• Keto Alfredo Soup
• Roasted Fennel with Radishes
• The Best Keto Fennel Recipes

📖 Recipe

StepAwayFromTheCarbs.com

Cauliflower Fennel Soup

4.70 from 10 votes

Roasted cauliflower and fennel blended with broth and a splash of cream into a silky, gently sweet low carb soup. Serve it with crunchy garlic crostini for a cozy lunch.

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Prep Time 10 minutes mins

Cook Time 30 minutes mins

Total Time 40 minutes mins

Makes: 2 servings

Net Carbs: 10

Calories: 301

Ingredients Equipment Method Nutrition Notes

Ingredients

 

US CustomaryMetric

For the Soup

• 10 oz raw cauliflower florets
• 1 small fennel bulb about 6 oz / 170 g, trimmed and chopped (save a few fronds for garnish)
• 2 tablespoon olive oil
• salt and black pepper
• 2 cups vegetable or chicken broth or bone broth
• ¼ cup heavy cream
• fennel fronds optional garnish

For the Garlic "Crostini" (optional)

• 12 low carb baked bagel chips
• 2 tablespoon butter softened
• 1 teaspoon garlic paste
• ½ teaspoon Italian seasoning

Equipment

• Aluminum Sheet Pan & Silicone Baking Mat Set, (Quarter Size)
• Ninja Professional 72oz Countertop Blender, Black
• AmazonBasics Silicone Baking Mat Sheet, Set of 2

Step-by-Step Instructions

 

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1. Preheat the oven to 400°F (200°C) and line a baking sheet with a silicone mat or parchment paper.
2. Spread the cauliflower florets and chopped fennel on the baking sheet, drizzle with the olive oil, and season with salt and pepper. Toss to coat, then roast for 20 to 25 minutes, turning once, until the vegetables are tender and browned at the edges.
3. Let the vegetables cool for 5 minutes, then transfer them to a blender. Add the broth and blend until completely smooth, venting the lid so the steam can escape.
4. Pour the soup into a saucepan over medium-low heat. Stir in the heavy cream, season to taste with salt and pepper, and heat for about 5 minutes until steaming hot (don't let it boil). Ladle into bowls and garnish with fennel fronds, if using.
5. To make the crostini (optional), heat the broiler. Mix the softened butter, garlic paste, and Italian seasoning in a small bowl. Spread it over the bagel chips, arrange them on a baking sheet, and broil for 1 to 2 minutes until the butter melts and sizzles. Watch closely so they don't burn.

Nutrition

Serving: 2cupsCalories: 301kcalCarbohydrates: 15gProtein: 6gFat: 26gSaturated Fat: 9gPolyunsaturated Fat: 2gMonounsaturated Fat: 13gTrans Fat: 0gCholesterol: 38mgSodium: 967mgPotassium: 849mgFiber: 5gSugar: 8gVitamin A: 556IUVitamin C: 79mgCalcium: 102mgIron: 1mgNet Carbs: 10g

Notes

Nutrition is for the soup only: one serving is half the recipe, about 2 cups, at roughly 10g net carbs. The garlic crostini aren't included, so add the numbers from your bagel chip label for six chips. Most low carb bagel chips are not gluten free.

For a lighter starter, split the soup into 4 bowls of about 1 cup each.

Store leftover soup in an airtight container in the fridge for up to 4 days, or freeze it for up to 3 months.

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Nutritional information is provided as a courtesy and is my best approximation. Net carbs are calculated as the total grams carbs minus the total grams of fiber.