Method:
Heat vinaigrette in a medium pot over medium high heat. Add carrots and two-thirds of the green onions and cook, stirring occasionally, until softened and lightly caramelized, 8 to 10 minutes. Add beans, 3 cups water, salt and pepper and bring to a boil. Reduce heat, cover and simmer until carrots are tender, 12 to 14 minutes more. Working in batches, carefully transfer contents of pot to a blender and puree until smooth. Return soup to pot and heat over medium low heat until hot throughout. Stir in sour cream, salt and pepper and serve, garnished with remaining green onions.