Preheat your oven to 400°F (200°C). Spread the cauliflower florets and whole garlic cloves on a baking sheet. Drizzle with a tablespoon of olive oil and toss to coat evenly, then roast for about 25-30 minutes until the cauliflower is golden and caramelized, and the garlic is soft and fragrant.
Remove the roasted cauliflower and garlic from the oven. Let the garlic cool slightly, then peel the papery skin off to reveal the soft, roasted cloves.
In a large pot, pour in the vegetable broth and bring it to a gentle simmer over medium heat. Add the roasted cauliflower and garlic to the broth, stirring gently.
Use an immersion blender to blend the soup directly in the pot until it is smooth and creamy. Alternatively, carefully transfer the soup in batches to a blender and purée until silky, then return it to the pot.
Taste the soup and season with salt and freshly ground black pepper as needed. If the soup is too thick, add a splash of hot vegetable broth and stir until you reach your desired consistency.
Heat the soup gently for a few minutes, just until heated through and the flavors meld. Serve hot, garnished with a drizzle of good olive oil or fresh herbs if desired.