As plantains ripen, their color changes from green to yellow to yellow mottled with brown-black spots to almost completely brown-black. Their flavor changes, too, from starchy to sweet, and they become softer in texture. For this recipe, the fruits should at least be well-mottled, so try to purchase ones that are already yellow, not green, and if needed, give them a few days to ripen. To peel plantains, trim off the ends with a paring knife, then use the tip of the knife to score the skin along its length. Pull off the peel with your hands; it will come away in sections, like a banana peel.