Preheat the oven to 350°F and tine a baking sheet with parchment paper.
In a large bowl, combine the cocoa powder, sugar, oil, eggs and vanilla extract and mix until incorporated.
Gradually add the remaining ingredients (except for the icing sugar) into the mixture and mix until just combined.
Cover the bowl with plastic wrap and chill in the fridge for at least 2 hours or overnight.
Roll the dough into round balls (about the size of a ping pong ball) and roll them in icing sugar. Place them on a lined baking sheet as you go on. If it the air is humid, you may have to reroll the balls into the icing sugar a second time.
Bake for 10 minutes or until the cookies have cracked nicely.
Cool before serving and enjoy!