In a large saucepan, saute onion and celery in oil until tender. Add the broth, carrots and potatoes; bring to a boil. Reduce heat; cover and simmer for 15-20 minutes or until vegetables are tender. Remove from the heat; cool slightly., Transfer to a blender; cover and process until blended. Return to pan; stir in salt and pepper. Heat through. If desired, sprinkle with cilantro.