While not nearly as sweet as bananas, plantains do have a sweet flavor. In this soup we keep that sweetness at bay by using firm plantains with green skins rather than riper brown-skinned ones--the sugars will have not yet developed, so the fruit will add starchy body to the soup without too much sweetness.
If you're unfamiliar with flan, think of it as a tasty variation on custard. One warning, though—it's very filling. A small slice of flan goes a long way! —Pat Forete, Miami, Florida