Add water and cauliflower florets to a large soup pot. Add onion, garlic, rosemary, sea salt, and black pepper. Simmer on medium/high heat for about 15 minutes. The cauliflower should be soft. Carefully blend the hot mixture in batches using a blender or an immersion blender. Taste for salt. Top with fresh parsley and olive oil before serving.
Recipe Notes
For an even richer flavor, substitute vegetable broth (or chicken if you're not vegetarian) for all or some of the water. A splash of coconut milk or heavy cream at the end would make it even more decadent.