In a medium bowl beat together the sugar and cocoa powder with the vegetable oil, before beating in the eggs and vanilla.
Combine the flour, baking powder & salt. Stir this through the wet mixture until it's smooth.
Transfer to a small bowl, cover with clingfilm and place in the fridge for at least 4 hours (or the freezer for 45-60 minutes, don't let it freeze).
Pre-heat the oven to 180°C and line a couple of baking trays with grease proof paper.
Using a tablespoon divide the dough out into balls. Roll each ball in icing sugar and place on the prepared trays. You'll need to do this in batches of about 6 per tray.
Bake for 10-12 minutes.
Place the tray on a wire rack and leave to cool for 5 minutes before removing from the tray and paper and leaving on the rack to cool completely.
Recipe by The Bearded Bakery at http://www.thebeardedbakery.com/baking/cookies/brownie-crackle-cookies-snowball-cookies/