If using fresh tomatoes, boil water in a 6 quart stock pot. Par boil tomatoes until skin splits, about 5 minutes. Remove tomatoes as they are done to large bowl. When cool enough to handle, core, peel, and roughly chop.
Using a 6 quart stock pot, add tomatoes, onion, celery seed, bay leaf and basil. Bring to a boil then reduce heat to simmer uncovered for fifteen minutes or until tomatoes are very soft; stir occasionally.
While the tomatoes are cooking, prepare Béchamel (white sauce).
When tomatoes are soft, puree using an immersion blender or in batches using a blender until very smooth. If there are a lot of seeds, remove using a food mill or sieve. There should be about six cups. If planning to freeze, freeze only prepared pureed tomato mixture and prepare white sauce later, after defrosting.