In a large mixing bowl, combine butter and sugar until light and fluffy.
Add eggs and vanilla and combine.
In a separate bowl, combine flour, cocoa powder, baking powder and salt.
Add dry ingredients into butter mixture. Mix until combined.
Remove dough from bowl and place on a sheet of plastic wrap. Form into a 6 inch disc and wrap completely with plastic wrap.
Refrigerate for at least 2 hours.
When dough is chilled through and firm, remove from fridge.
Form into balls. Place the balls into a bowl of powdered sugar. Roll each ball around until covered with powdered sugar. Place on an ungreased baking sheet.
Bake in a preheated 350 degree oven for 12-15 minutes.
Let cookies cool for a few minutes on baking sheet. Remove and place on a cooling rack until completely cooled.