This creamy tomato and summer herb soup takes less than 25 minutes to prepare and can be served hot or cold. I prefer it hot. It is bursting with flavor and contains a full serving of vegetables in each bowl. Tarragon is the herb of choice in this version of the recipe, but chopped basil or even mint would work, too. While some creamy soups are made with heavy cream or sour cream, this one gets a rich, tangy flavor from a modest amount of reduced-fat sour cream. If you like, you can use low-fat plain yogurt instead. The soup is best when made with ripe tomatoes, but a 28-ounce can of diced tomatoes with their juices can be substituted in a pinch. For a complete light meal, serve this soup with a salad and a few slices of grilled whole-grain baguette.