Preheat the oven to 350 F. In a large bowl, combine butter with powdered sugar until fluffy. Add in the vanilla extract, and mix until smooth.
Add in the flour and cocoa powder. Mix until it is fully combined. Roll the cookie dough into balls, and place onto a large ungreased baking sheet. Bake for 10-12 minutes.
Place the remaining powdered sugar into a shallow dish. Roll each cookie into the powdered sugar.