1. Finely chop the onion, carrot, celery and garlic. Heat the olive oil in a large saucepan and cook the chopped vegetables over medium heat until soft but not brown, about 3 to 4 minutes. Add the stock and bring to a boil.
2. Peel and thinly slice the plantains. Add the plantains, bay leaf, cumin, half the cilantro, salt, and pepper to the stock. Bring to a boil, reduce the heat, and gently simmer the soup until the plantains are very tender, 30 to 40 minutes.
3. Remove the bay leaf and puree the soup in a blender. If necessary, thin with a little stock. Just before serving, heat the soup and correct the seasoning, adding salt or cumin as necessary. Sprinkle with the remaining cilantro and serve at once.Serving Size: approximately 1 cup