Preheat oven to 350 degrees F.
In a large bowl, combine the butter and sugar, beating until fluffy.
Add eggs one at a time.
Gradually add the cocoa powder and flour, blending thoroughly.
Cover and chill for at least one hour.
Shape into balls about the size of a tablespoon.
Roll each ball in the powdered sugar and place on parchment paper.
Bake for 12 minutes
Allow cookies to cool for 5 minutes before removing and place on a rack to finish cooling.
Sprinkle with more powdered sugar if you wish!