Heat oil in a large saucepot over medium high heat. Add carrots, onions and garlic and saute until vegetables are fragrant and translucent, about 3-4 minutes.
Add stock, milk, salt, pepper and ground powdered ginger.
Bring soup to boil, reduce heat, and let simmer for 20 minutes.
Add grated ginger root. Turn off heat and cover pot. Let steep for 5 minutes.
Puree soup in batches in a blender, carefully avoiding spills that can burn you.
Serve hot or cold. Garnish with sour cream if desired.