Tostones are a Cuban specialty in which unripe plantain rounds are fried once, then flattened with the back of a skillet, and fried again until golden brown. It is traditionally served with mojo, a spicy dipping sauce.
You will need sweet, fully ripened plantains (platanos maduros, in Spanish) for this Cuban-inspired side dish. They are soft, with peels that are mostly brown or black. Plantains are available in Latin-American markets and many grocery stores.