Preheat oven to 400°. Individually wrap the plantains, with their skin on, in aluminum foil and place on a baking sheet in the oven. (Some people bake them without the aluminum foil, so you can try it both ways)

Bake for about 25 minutes, until plantains are completely cooked through, and very soft. Carefully open up the foil by making a slit down the middle, and pour the condensed milk (or topping of your choice) on top.