In a large saucepan, heat oil over medium heat. Add onion and curry. Cook, stirring frequently, until onion has softened and mixture is very fragrant (about 5 minutes). Add carrots, broth, coconut milk, cilantro and salt. Cover and bring to a boil. Reduce heat and simmer, stirring occasionally, until carrots are very tender, about 30 minutes. Meanwhile, peel and slice mangoes (if fresh) away from stones. Coarsely chop. Purée in a food processor until very smooth. Place in a small bowl and put aside. When carrots are tender, remove from broth and purée in batches using a little of the broth. Return purée to remaining broth in saucepan. Stir in mango purée. Heat over medium-low heat, uncovered and stirring often, until hot, about 5 minutes. Serve hot or refrigerate and serve cold. Soup can be frozen or will keep, refrigerated, for
3 days.