Heat olive oil in a large pot. Add onions and garlic and saute until soft. Add celery, cauliflower, salt, pepper, and bay leaves. Stir well and saute until all the vegetables soften, about 20 minutes. You can turn the heat to medium-low, cover the pot, and let the vegetables sweat it out for a bit, too.
Add water or stock until it just barely covers the vegetables. Bring to a boil, then reduce heat to a simmer, cover, and let cook another 20 minutes. When you lift the lid, everything should be soft and fragrant.
Turn off the heat and add the finely chopped green celery leaves and parsley. Stir until just blended in. Then use a blender or immersion blender to puree the soup until very smooth.
Pour into the same (rinsed) pot. Taste for salt and pepper.
You can serve hot (do not bring to boil, just gently heat), or let cool, then chill in the refrigerator and serve chilled.
To garnish, blend the parsley with 1/2 the oil and harissa/hot sauce with the other half. Drizzle in..and eat
