Place a fine strainer over a bowl and seed the tomatoes into the strainer. Scrape the seeds against the strainer, extracting as much liquid as possible; discard the seeds. Chop the remaining tomato flesh; add half of the chopped tomato to the tomato liquid.
In a large saucepan, melt the butter over medium heat. Add the onion and cook, stirring occasionally, until softened, about 5 minutes. Add the remaining chopped tomato and the brown sugar; cook, stirring, until the tomatoes break down, 10 minutes. Add the chicken broth and 2 cups water. Whisk in the breadcrumbs and simmer for 5 minutes; season with salt.
Using a food processor, and working in batches, puree the soup. For cold soup, refrigerate until chilled.
In a bowl, whip the cream until soft peaks form. Fold in the pepper. Dollop on top of the soup.