In a heavy soup pot or Dutch oven, heat 2 tablespoons olive oil over medium-low. Add the chopped onion and cook until translucent and softened; 5 to 6 minutes. Add the garlic and cook for another 30 seconds, or until fragrant.

Pour in the vegetable stock and add cauliflower, salt, turmeric, cumin, and red pepper flakes. Bring to a boil over high heat. Reduce the heat, cover, and simmer until the cauliflower is tender; about 10 minutes.

In batches, blend the soup with 2 tablespoons of butter on high until creamy. Add salt and pepper to taste and rewarm the soup if necessary. Add additional broth to thin to your desired consistency.

Serve the soup warm and garnished with a roasted cauliflower floret and chopped parsley if desired.