Prepare the dough: In a large bowl, whisk together cocoa powder, sugar and oil. Then add remaining ingredients and mix for 2-3 minutes, until fully combined.
Let it chill: Cover the bowl with plastic foil and refrigerate the dough for at least 3 hours or overnight. This helps thicken the dough and helps create the classic crinkle design when in the oven.
Roll in icing sugar: Fill a bowl with icing sugar. Take about 1 tbsp per cookie and use another spoon to push it into the icing sugar. Toss the dough around and start rolling into a ball. Repeat for all cookies, they should have about the size of a walnut.Tipp: Before baking the cookies, make sure they all still have a white layer of icing sugar. Given humidity or moistness of the dough, the icing sugar might slightly fade. You may need to double coat them in icing sugar - the thicker the icing sugar layer, the more prominent the crinkle pattern will be.
Bake & enjoy: Bake the crinkle cookies on 180C (356 F) for 10 minutes. Let cool and store in an airtight box. Enjoy!