Heat oil in a large saucepan over medium heat. Add onion and garlic; sauté 5 minutes. Stir in 1 tablespoon coriander. Add chicken broth and carrot; bring to a boil. Cover, reduce heat, and simmer 15 minutes or until carrot is tender. Let cool slightly.
. Transfer mixture in batches to a blender or food processor, and process 1 minute or until very smooth. Stir in 2 tablespoons lime juice and salt. Set aside.
. Combine sour cream, cilantro, remaining 1 teaspoon lime juice, and remaining 1/8 teaspoon coriander in a small bowl. Ladle soup into bowls, and top with sour cream mixture.