Put into a granite-ware saucepan the canned or fresh tomatoes; add the water or stock; the soup will be better if stock is used; add also the bay-leaf, parsley, celery, peppercorns, and sugar; simmer until the tomato is thoroughly soft. In another saucepan put the butter; when it is hot add the onion, and fry, but not brown it; then add the flour, and cook, but not brown the flour. To this roux add enough of the tomato to dilute it, and then mix it well with the rest of the tomato, and season with salt. Pass the whole through a fine sieve or strainer. Heat it again before serving, and sprinkle over the top small croutons.