In a 6-quart pan, over medium high heat, add butter and onions and cook until limp.
Add chicken broth, carrots, and ginger. Cover and bring to boil. Reduce heat until carrots are fork tender.
Remove from heat and transfer to blender. Pulse blender to and puree until smooth. Return to pan and add whipping cream and stir over high heat until hot. Add salt and ground black pepper to taste.
Ladle into bowls and garnish with dollop of sour cream and parsley.