From http://www.recipesource.com/text/soups/soups/recipe1322.txt, Joanne Weir
This is a very easy and delicious soup. I modified it by adding the 1/2 cup of basil leaves to the puree, instead of using that as garnish. You could probably also add garlic to the onion, when it's sauteeing.
Heat the olive oil in a large soup pot over medium-high heat. Add the onion and cook, about 7 minutes. Add the basil sprigs, tomatoes, chicken stock and 1 cup water and bring to a boil over high heat. Reduce the heat to medium-low and simmer until the liquid is reduced by one-quarter, about 20 minutes. Cool for 10 minutes. Remove the basil and discard.
(ed. note: at this point, I added the cut-up basil to the tomato mixture.)
In a blender, puree the soup in several batches until smooth, 2-3 minutes per batch. Strain into a clean pot (ed. note: well, I used the same pot) and bring to a simmer over medium heat. Season to taste with salt and pepper.
To serve, ladle the soup into bowls and garnish with basil leaves.
Note: This soup can be made up to a day in advance and stored in the refrigerator until ready to serve. Reheat over medium heat until hot, about 5 minutes.
Serves 6. Per serving: 88 calories, 4 grams fat.