Place medium to large non-stick saucepan on medium heat.
Melt butter in the saucepan. Add onion and ginger and stir fry or sauté for 2 minutes.
Add carrots, vegetable broth or water, salt and pepper. Cover. Lower the heat to Low. Cook for about 15 minutes or until carrots are tender. Let it cool a little.
In a blender or food processor, purée the carrot-broth mixture. Transfer the contents to the saucepan on low heat.
Stir in the sour cream into the saucepan.
Serve the soup hot.