Preheat the oven to 400 degrees F (200 degrees C). Line a baking sheet with parchment paper.

Place cauliflower florets on the prepared baking sheet and toss with 2 tablespoons olive oil. Cut the top off the garlic bulb crosswise to expose the cloves; drizzle with remaining 1 tablespoon olive oil, and wrap it in aluminum foil. Place wrapped garlic bulb on the baking sheet with cauliflower.

Roast in the preheated oven until cauliflower is golden brown and garlic is soft, about 30 minutes. Cool garlic and squeeze roasted cloves from their skins.

In a blender, combine cauliflower, garlic cloves, vegetable broth, and truffle oil. Blend until smooth. Pour into a large saucepan and bring to a simmer for 8 to 10 minutes. Add heavy cream and stir to combine. Season to taste with salt and pepper.