Heat oil in heavy large saucepan over medium-high heat. Add onion, garlic and 1/4 cup minced ginger and saute until onion is translucent, about 8 minutes. Add 4 cups chicken stock and 4 cups sliced carrots. Cover and simmer until carrots are tender, about 30 minutes.
Working in batches, puree mixture in blender or processor. Return soup to saucepan over low heat. Mix half and half and curry. Season soup to taste with salt and pepper.