In a large bowl, mix cocoa powder, sugar, and butter until smooth.
Beat in the eggs one at a time, then stir in the vanilla.
In a separate bowl, whisk together flour, baking powder, and salt.
Gradually add the dry ingredients into the wet mixture until fully combined. The dough will be thick and sticky.
Cover and chill the dough in the firdge for at least 4 hours or overnight (this step helps create the classic crinkle effect)
Preheat over to 350 F (175 C). Line baking sheets with parchment paper.
Scoop tablespoon sized portions of dough and roll into balls.
Roll each ball generously in icing sugar, coating all sides.
Place about 2 inches apart on the baking sheet.
Bake for 10-12 minutes, just until they puff up and the tops crack. Don't overbake. They should be soft inside.
Let cool on the pan for a few minutes before transferring to a rack.