Melt butter in heavy large pot over medium-high heat. Add carrot and next 6 ingredients and sauté until vegetables are soft, about 10 minutes.
Discard bay leaf. Transfer mixture to processor and blend until smooth. Return mixture to pot. Add broth and all remaining ingredients except cilantro sour cream. Boil soup over medium-high heat 15 minutes to blend flavors.
Cool slightly. Working in batches, puree soup in blender until smooth. Return soup to pot. Season to taste with salt and pepper. (Can be made 1 day ahead. Cool slightly, then cover and refrigerate.)
Bring soup to simmer. Divide among 8 bowls. Sprinkle with cilantro and serve.
* Percent Daily Values are based on a 2,000 calorie diet. Your daily value may be higher or lower depending on your calorie needs.