Gather all of the ingredients you need for this recipe and preheat your oven to 400F. You'll also need to line a baking sheet with parchment paper.
In a bowl, add the following ingredients: both types of flour, corn starch, salt, baking powder and baking soda. Mix well and leave to one side.
Add your cubes of butter to a mixer and beat well on a medium setting. After around 30 seconds, add the brown sugar, and then the white sugar; mixing as you go.
Once your butter mixture is fluffy, add your egg, egg yolk and vanilla. Stir until evenly distributed throughout the batter.
Slowly add the bowl of dry ingredients to your butter mixture. Once completely combined, fold in your chocolate chips.
Shape your cookies into slightly flattened balls and drop onto your prepared baking sheet. Place in the center of your preheated oven for around 10-12 minutes.
Remove cookies from the oven and leave to cool before serving. Serve and enjoy!