1. Peel the plantains: Cut off the ends using a sharp knife, score the skin on four sides, then use your fingers to pry the skin loose.
2. Cut peeled plantains into one-inch pieces. Fry them in a skillet in the vegetable oil over moderately high heat for five minutes, then set them out on paper towels to drain and cool slightly.
3. Smash each fried plantain to a quarter-inch thickness with a tool called a tostonera . You can also use a mallet or the heel of your hand.
4. Soak the plantains in salty water for one minute; they'll emerge perfectly seasoned. Set them out on paper towels to drain.
5. Fry the tostones again for five minutes until crisp; drain them on paper towels and season with a little bit more salt before serving. They're delicious with a squirt of fresh lime juice, too.