1. Preheat the oven to 425°F. Line a large rimmed baking sheet with parchment paper for easier cleanup.

2. Place the cauliflower florets on the baking sheet. Drizzle with 2 tablespoons olive oil, sprinkle lightly with salt, and toss until coated. Spread into a single layer. Roast for 25 to 35 minutes, stirring halfway through, until tender and golden around the edges.

3. When the cauliflower is nearly done, heat the remaining 1 tablespoon olive oil in a large soup pot over medium heat. Add the onion and 1/4 teaspoon salt. Cook for 5 to 7 minutes, stirring occasionally, until softened.

4. Add the garlic and cook for about 30 seconds, stirring constantly. Pour in the vegetable broth.

5. Set aside a few roasted cauliflower florets for garnish. Add the rest of the roasted cauliflower to the pot. Bring to a simmer, then reduce the heat and cook gently for 20 minutes.

6. Remove the pot from the heat and let the soup cool slightly. Carefully blend the soup in batches until smooth. Add the butter, lemon juice, and nutmeg, then blend again until creamy.

7. Taste and adjust with more salt or lemon juice as needed. Serve warm, topped with reserved roasted cauliflower and fresh herbs.