In a medium stockpot over medium-high heat, sauté onion, carrots and leeks in drizzle of olive oil, 5-7 minutes or until onions are translucent.
Add chopped cauliflower and salt and pepper to taste, combine.
Add water (700 mL/3 cups or so), cover and simmer on medium-low heat 20 minutes making sure cauliflower is tender.
Strain and set apart some of the vegetable broth, then using an immersion blender, purée vegetables, adding broth back a little at a time to desired consistency. Adjust salt and pepper to taste.
Serve with topping of choice, such as chopped fresh herbs or whole grain croutons.
Notes
I purposely don't include cream for this healthier version of cream of carrot soup, but it is optional.