Cube the cold butter and add it to a mixer. Mix for 1 minute to break up the butter.
Add the caster sugar and light brown sugar to the mixer and mix for 30 seconds to combine.
Add the 450g of dark chocolate chips to the mixer and mix for another 30 seconds.
In a separate bowl, combine the 230g self-raising flour, 200g plain flour, 70g cocoa powder, 1 tsp salt, ¼ tsp bicarbonate of soda, and 3 tsp baking powder.
Add the dry ingredients to the mixer and mix until it reaches a breadcrumb consistency.
Lightly beat the 2 large eggs and 1 egg yolk, then add them to the mixer and mix until the dough comes together.
Scoop 125g balls of dough, gently press them together, and place them on a board.
Wrap the dough balls in cling film and freeze for 90 minutes or overnight.
Preheat the oven to 180°C with a baking tray inside to get hot.
Bake the cookies for 18 minutes until the edges are crispy and the centers are still soft.
