Preheat the oven to 400°F (200°C). Cut the top off the garlic bulb, drizzle with olive oil, wrap in foil, and roast for 30-35 minutes until soft.

Once roasted, let it cool slightly, then squeeze the garlic cloves out of their skins and set aside.

In a large pot, heat olive oil over medium heat. Add chopped onion, celery, and carrot. Sauté for about 5-7 minutes until softened.

Add cauliflower florets, roasted garlic, vegetable broth, salt, pepper, and thyme. Bring to a boil, then reduce heat and simmer for 20 minutes until cauliflower is tender.

Using an immersion blender, blend the soup until smooth. Alternatively, transfer to a blender in batches.

Stir in heavy cream and shredded cheddar cheese until melted and combined. Adjust seasoning if necessary.

Ladle the soup into bowls and garnish with additional cheddar cheese or fresh herbs if desired.