Sweet Potato and Rosemary Soup

In a large saucepan heat oil over medium heat. Add onion and garlic; cook and stir about 5 minutes or until onion is tender. Add carrot, celery, thyme, and rosemary. Cook and stir for 3 minutes more. Add potatoes and broth. Bring to boiling; reduce heat. Simmer, covered, for 25 minutes. Cool slightly. Remove half of the mixture (about 3 1/2 cups) to a large heatproof bowl. Place half of the mixture in the bowl in a blender or food processor. Cover and blend or process until smooth. Return to mixture in saucepan. Place remaining mixture in bowl in blender or food processor. Process until smooth; return to saucepan. Heat through.