Pre-heat the oven to 190°C and line a large baking tray with grease-proof/baking paper.
Beat the olive oil and sugar together, then beat in the egg. In a separate bowl mix flour, baking soda, baking powder, vanilla sugar, cocoa powder, chocolate and salt.
Add the wet ingredients to the dry, and stir to combine everything together. The end result should be a dough you can easily handle.
Roll into balls of equal size and place each one on the baking tray with a little space apart. Push down with the back of a fork to flatten a little. Bake for around 12 minutes (until the edges are firm).
Remove from the oven and leave on the tray for a while, then transfer to a wire rack to cool completely. When cold, sprinkle with a little icing sugar (if using) and enjoy!