Make the brown butter: Add the butter in a saucepan and melt it on medium heat. Mix the butter with a spatula until it's completely melted and comes to a boil. After a few minutes, the milk solids will separate and the butter will start resembling dish soap; this means you are close. Soon, the butter will start to foam up. Keep mixing until you see streaks of brown in the foam. This means that the butter has started browning, and you will also be able to smell a nutty aroma. Once the brown streaks appear, cook for 1-2 more minutes and take it off the heat. Keep a close eye on the butter once it starts foaming, as it can burn very easily. You want to toast the milk solids but not burn them. Transfer the butter to a heat-proof bowl immediately to stop the cooking process. Let it cool to room temperature.
Mix all the dry ingredients in a bowl: all-purpose flour, cornstarch, baking soda, baking powder, and salt.
Add the brown butter and both white and brown sugars and mix together on high speed for 2 minutes until well combined.
Next, add the eggs and vanilla essence to the batter and whisk until well combined. Make sure the eggs are fully incorporated into the butter, and there is no liquid left in the batter
With the mixer on slow, add the dry ingredients into the batter and keep mixing on slow until everything is well incorporated and there are no streaks of flour still remaining in the mix. You will have a nice, thick dough at this point.
Finally, add the chocolate and mix it into the dough with a spatula until just combined.
Wrap the prepared dough in cling film and refrigerate for 12-48 hours.* I know that’s a long wait, but trust me, it’s totally worth it! When you’re ready to bake, take the cookie dough out of the fridge and bring it to room temperature.
Preheat your oven to 180 degree Celsius and prepare your baking pan by covering it with baking paper. Scoop out cookie dough balls on your baking tray. I use an ice cream scoop to scoop out the cookie dough because it gives evenly sized and shaped cookies every time. If you don’t have an ice cream scoop, measure the dough using a regular tablespoon and shape it into balls before placing it on the baking tray.
Bake the cookies for 12-14 mins. Properly baked cookies should have browned from the sides but should still be soft from the center. Don’t worry; they’re not raw from the center! The cookies keep cooking from residual heat even after you take them out of the oven. Taking them out while the center is still soft ensures that the cookies have a soft and chewy middle.
Pro tip: If you want your cookies to have that perfect round bakery look, take a round cookie cutter, mug, or jar lid and shape your cookies as soon as they come out of the oven. Because they are still soft, this technique helps shape the cookies and push all the chewy goodness to the center.
To finish, top the cookies with more chocolate and a sprinkle of sea salt. Enjoy warm.