Melt butter in a small saucepan over low heat, stirring occasionally. Alternatively, melt in microwave in 30-second intervals.
Pour melted butter into a large mixing bowl and set aside to cool for 5-10 minutes until it’s only slightly warm. Don’t let it firm back up again.
Add both sugars and whisk for 20 seconds until well combined. NOTE: The mixture will thicken gradually; avoid leaving it too long, as it will become harder to whisk the egg in the next step.
Add egg and vanilla, whisk until well combined, about 15 seconds.
Sift over flour, cornstarch and baking soda. Add salt.
Using a rubber spatula or wooden spoon, fold and mix until a cookie dough forms, about 40 seconds, it will be thick.
Add chocolate chips and gently fold through until distributed.
Chill cookie dough in refrigerator for 45 minutes, or if the bowl is too large, wrap the dough and refrigerate without the bowl. *For overnight chilling, see notes below.
While dough chills, preheat oven to 180ºC (356ºF). Line a large baking sheet with parchment paper and set aside.
After 45 minutes, remove dough from fridge.
Working one cookie at a time, scoop and weigh 50g (1.7oz) of dough and roll into a ball. NOTE: Without a food scale, use 3 level tablespoons per cookie.
Flatten slightly in the palm of your hand to create a thick disc.
Place one caramel candy in centre of cookie dough disc.
Press dough around caramel to cover it then roll into a smooth ball. IMPORTANT: Keep that caramel near the top of the dough ball. Otherwise, it'll make a gooey escape out the bottom, sticking to your parchment paper.
Place dough ball on lined baking sheet. Repeat with remaining dough, spacing cookie balls 10cm (4 inches) apart to allow for spreading, and leaving gaps near tray edges. Bake in batches, as they won't all fit on one tray.
Bake for 10-12 minutes until edges are lightly golden. Centers may look slightly under-baked; that's what keeps them soft and chewy.
Remove from oven and tap baking sheet on your bench top or stovetop 3 times to help slightly deflate.
Allow cookies to cool on sheet for 15 minutes.
If some caramel oozed out the bottoms, use a slotted turner to lift them off the parchment paper and transfer cookies to a wire rack to cool completely. They’ll still be soft and delicate so handle with care to avoid breakages.
Enjoy!