In a mixing bowl, cream together the sugars, vanilla, salt and butter until light and fluffy.

Add in the two egg yolks and mix.

Add in your flour and cocoa and mix until a pliable dough is formed.

Add in most of your chocolate and stir to combine (save some for later!)

Place the dough in the fridge for a minimum of 30 minutes to chill.

Preheat your oven to 170°C (Fan) or 180°C (non fan).

On a lined baking tray, add golfball sized balls of dough. Top with some chocolate saved from before.

Bake in the oven for 10 minutes. Take out of the oven and leave to cool completely (the cookies will set as they cool, do not overbake!)