Wrap the potatoes with a moistened kitchen towel.
Wrap in plastic wrap.
Microwave at 500 W for 4 minutes. Flip it over and microwave for another minute. (If it is still hard, microwave a little more at a time.)
Make two scores on top of the potatoes in a crosshair pattern, top with butter, and enjoy.
Story Behind this Recipe
Just wrapping in plastic wrap before microwaving will cook it unevenly, so in order to properly steam it, I tried wrapping it in a moistened kitchen towel as well.
If you microwave it for too long, you can't go back and fix it, so heat just a bit at first and then heat a little more at a time if it's still too hard. The amount of time needed will depend on the size of your potatoes.