Melt butter then set aside to cool for 10-15 minutes until it’s only slightly warm. Don’t let it firm back up again.
Pour butter into a large mixing bowl. Add both sugars and using a handheld whisk, whisk for 20 seconds until well combined, it will slowly start to thicken and the longer you leave it, the thicker it will get, so be sure not too leave it sitting for too long as it will be harder to whisk through your egg in the next step.
Add egg and vanilla, whisk until well combined, about 15 seconds.
Sift over flour, cornstarch and baking soda. Add the salt. Fold and mix with a spatula or wooden spoon until well combined and a soft cookie dough begins to form, it will be thick.
Add chocolate chips and fold/mix until chips are throughout the dough.
Transfer bowl with cookie dough inside to the refrigerator and chill for 1 hour. You can also chill your dough overnight, if do you, remove your dough from the fridge 30 minutes before you create the cookies. If your bowl is too large for the fridge, just wrap your dough directly and place it in the fridge without the bowl.
Whilst dough is chilling, preheat oven to 180ºC (350ºF). Line a large flat baking tray with parchment paper, set aside.
Remove dough from fridge.
To create, weigh out each cookie to be 50g (2oz). If you don’t have a food scale, measure each cookie to be 3 level tablespoons. I highly recommended you use a food scale to measure each one.
Place onto lined tray, leaving as tall balls, do not flatten.
Repeat with remaining dough, leaving a gap of 10cm (4 inches) between each cookie ball on tray to allow for spreading, also leaving a bit of gap between the balls and the edges of the tray. You will have to bake your cookies in batches as they won’t all fit on one baking tray.
Bake for 10-12 minutes or until golden around the edges and lightly golden in the middles. The centre of each will still look slightly under-baked which is great, that’s what makes them soft and chewy.
Remove from oven and gently tap the baking tray on your bench top or stove top 3 times to help slightly deflate. Allow cookies to cool on tray for 15 minutes.
Carefully transfer cookies to a wire rack to cool completely. They’ll still be soft and delicate so handle with care to avoid breakages.
Cool completely on rack or allow one to firm up a little to enjoy a warm cookie whilst the choc chunks are still gooey, delicious!
Store in an airtight container, in a dark dry pantry for 1 week. Refer to notes for freezing instructions.
Enjoy!