Bring the tomatoes, carrots and onion to a boil over medium-high heat in a stockpot then reduce heat to medium-low. Simmer for 30 minutes. Stir in the chicken broth, sugar and salt.
Melt the butter over medium-low heat in a small saucepan. Whisk in the flour, stirring until thick. Slowly whisk in the milk until smooth. Cook and stir, whisking constantly until thickened, about 5 minutes. Stir milk mixture in to the stock pot. Season with basil, celery salt, black pepper and garlic powder. Continue to simmer the soup on low to reduce and thicken, about 1 hour.
For a smoother soup
A food processor can be used to finely chop the carrots and onion. A stick blender can be used for a smooth texture.