Heat the oil in large Dutch oven over medium heat. Add the onions and gingerroot. Cook and stir for 2 minutes.
Add all the remaining ingredients except for the sour cream and parsley. Bring to a boil. Cover and reduce the heat. Simmer for 30 to 35 minutes or until the carrots are very tender.
Carefully blend the soup in batches in a blender and return to the Dutch oven or use an immersion blender to blend the soup in the pot. Stir in 1 cup of the sour cream.
Dollop each serving with the remaining sour cream and garnish with parsley sprig.