Preheat oven to 425F or 230C, cut cauliflower into slices, and spray with olive or vegetable oil and roast until the cauliflower start to caramelize and turn black. About 30 minutes (Reserve 1/3 to garnish with add 2/3 to the soup)
In a large pot over medium-high heat, heat the oil and sauté the onion for about 15 minutes, stirring occasionally, until soft and golden.
Add the garlic and curry paste and cook for another 5 minutes, stirring frequently, until fragrant.
Add the cauliflower, broth, salt, and pepper and bring the mixture to a boil. Then reduce the heat and simmer for about 10 minutes to let the flavors come together.
Carefully transfer the soup to a blender and blend until smooth and creamy. You may need to do this in batches, depending on the size of your blender. Alternatively, you can use an immersion blender to blend the soup in the pot. (Less cleanup)
Return the soup to the pot and stir in the coconut milk and lemon juice. Taste and adjust the seasoning if needed.
Ladle the soup into bowls and garnish with fresh herbs. Enjoy!