Lightly spray heated nonstick stock pot with vegetable oil spray. Sauté onions in stock pot at medium-high heat. Add carrots, celery, and potatoes. Lower heat and sweat for 10 minutes.
Add stock, coriander, and pepper. Cook on medium heat till vegetables are tender, about 45 minutes; then puree.
Add cilantro and milk. Bring to a boil and serve.
Freeze what you don’t eat today in single-serving containers for easy-to-thaw-and-heat-up soup for future snacks and meals.