Preheat your oven to 425°F. Cut the cauliflower into 1-inch florets and toss with 3 tablespoons of olive oil, salt, and pepper on a baking sheet, spreading them in a single layer for even browning. Wrap the whole garlic head in foil with the remaining 1 tablespoon of olive oil, salt, and pepper. Place both on the baking sheet and roast for 35-40 minutes until the cauliflower is golden brown and tender, and the garlic is soft and caramelized. If the garlic needs more time, continue roasting for another 10-15 minutes. Once done, squeeze the roasted garlic cloves out of their skins—they should slip out easily.

While the vegetables roast, melt the butter in a large pot over medium heat. Add the diced onion and cook for 5-6 minutes, stirring occasionally, until softened and translucent. After about a minute, add the thyme and bay leaf, stirring constantly for 30 seconds to bloom the herbs and release their essential oils—this is key for building deep flavor in the broth. I like to bloom herbs this way because it distributes them evenly throughout the soup rather than having bits of herb floating around.

Pour the vegetable broth and chicken broth into the pot with the onion mixture and bring to a boil over medium-high heat. Once boiling, add the roasted cauliflower and roasted garlic cloves from Step 1, then immediately remove the bay leaf. Reduce the heat to medium and let everything simmer together for a few minutes to allow the flavors to meld.

Using an immersion blender, carefully blend the soup until smooth and creamy, working in batches if needed. I recommend leaving a few small cauliflower pieces unblended for texture—it makes the soup more interesting than a completely smooth puree. Simmer the blended soup for 5 minutes over medium heat to help the flavors come together. Meanwhile, make sure your cream is at room temperature (around 70°F) so it won't break or curdle when added to the hot soup.

Remove the pot from heat and slowly stir in the room-temperature cream until fully incorporated. Add a pinch of ground nutmeg—it's a classic pairing with cauliflower that adds subtle warmth and depth. Finish with the truffle oil if using, which adds incredible richness and an earthy note that elevates the dish. Taste and adjust seasoning with additional salt and pepper as needed. I use Kerrygold butter and good quality broth because they make a real difference in the final flavor—these are worth investing in for a soup like this.