Start by beating the cold butter on medium for 30 seconds to break it up; do not cream it.
Add in the sugars and beat again to combine with the butter, forming little nuggets.
Mix in the chopped chocolate until evenly distributed.
Pour in all sifted dry ingredients and mix until a dry, bread crumb consistency forms.
In a separate bowl, whisk the eggs and egg yolk with a fork, then add to the batter and beat until just combined.
Divide the dough into about 13 squished, uneven balls, each approximately 125g in size.
Cover the dough balls with plastic wrap and freeze for at least 90 minutes, preferably overnight.
Place the frozen dough balls directly onto a baking tray and bake at 180°C (fan) for 18 minutes.
Allow cookies to cool for at least 10 minutes on the tray before removing.