To a stockpot, add tomatoes, broth, celery, carrots, herbs and salt. Bring to a boil and then simmer covered for about half an hour or until the celery and carrots are no longer crunchy.
In separate sauce pan, melt butter and saute onions and garlic until soft. Slowly add flour to create a roux.
Once the flour is completely absorbed into the butter, slowly add tomato broth from the larger pot to the roux. Be sure there are no lumps before adding more. You cannot get the lumps out later. Continue adding tomato base until it is thin, once your roux has been thinned to a sauce-like consistency, you can add it back into the larger pot. Bring to a boil and then simmer for 5 minutes to an hour.
Use an immersion blender until the soup is smooth or process in a food processor or blender in batchs.
