Heat the olive oil (or other cooking fat of your choice) in a large stock pot set over medium heat. Add the onion, celery, salt and pepper and cook until slightly softened and fragrant, about 3 minutes.Add the garlic powder, onion powder, celery seeds, about 7 cups of the broccoli florets, all of the cauliflower florets and chicken broth; cover loosely and cook until the cauliflower and broccoli florets are fork tender, about 8 to 10 minutes.Carefully ladle about half the soup into a High-Speed Blender; process until smooth and creamy and transfer to a clean container. Repeat as many times as necessary with the rest of the soup.Once all the soup has been processed, return it to the stock pot; Chop the remaining cup of broccoli florets really finely and add that to the soup, along with the cup of milk. Stir, bring back to a simmer over medium heat then kill the heat and serve promptly.