In a saucepan, combine cauliflower, celery and broth. Bring to a boil over high heat. Reduce heat and simmer for 10 minutes or until vegetables are tender. Working in batches, transfer soup to blender (or use immersion blender in saucepan) and puree until smooth.
Return soup to saucepan (if necessary) and stir in milk and white pepper. Heat over medium heat, stirring occasionally,until hot (do not let boil). Ladle into warmed bowls and garnish with green onion.
Notes: Instead of store bought chicken broth, you can use home made chicken stock. You may need to add 1/4 teaspoon of salt to enhance the taste of the soup. Taste the soup and add just enough salt to perk up the flavor. Heat milk based soup just to a simmer or it may curdle.