Ripen them quickly by placing your unpeeled whole bananas on a lined baking tray. Bake them in a 300ºF (150°C) oven for 20 to 25 minutes, or until the skins are completely black. Remove from the oven and allow to cool on the tray. Once cool you can use them in any recipe that calls for ripe, spotty bananas. Simply slit the skins with a sharp knife and scoop the soft flesh out with a spoon.