Boil all for an hour then sieve well. Return to pot.
Mix flour and butter to a smooth paste then add to soup. Boil for a further 10 mins. Either bottle while still hot or cool and freeze.
When you reheat it, do so very gently. You can add either milk or water at this stage to thin it a little.
Goes well with a swirl of cream and chopped parsley on top.
This also can be used instead of tomato puree in other recipes.