Heat the olive oil in a large pot over medium heat. Add the onion, carrot, and celery. Cook for 5 minutes, stirring frequently.
Add the garlic, cumin, salt, and black pepper. Cook for 1 minute, stirring constantly.
Stir in the sliced plantains.
Pour in the chicken broth and add the bay leaf. Stir well, gently scraping up any bits from the bottom of the pot.
Raise the heat to high and bring the soup to a boil (about 4–5 minutes). Once boiling, reduce the heat to medium-low and simmer for 35–40 minutes, or until the plantains are tender. Stir occasionally, lowering the heat if needed as the soup thickens.
The plantains should be soft enough to break apart with a wooden spoon. If they’re still firm, continue cooking for another 10 minutes, then check again.
Remove and discard the bay leaf. Taste and add salt if needed. (As a reference, we did not add any extra salt to ours.)
Serve the soup as is, or process it for a smoother texture. We used an immersion blender to blend it directly in the pot. For a chunkier texture, use a potato masher to mash some of the plantains while stirring. (Whether blending or mashing, remove the bay leaf first, take the soup off the heat, and let it stop simmering before proceeding.)
Garnish with chopped cilantro (or parsley) and crushed plantain chips, and serve with lime wedges, if desired.