Start by melting and browning the butter in a pan over medium heat. Stir constantly until it turns brown and releases a nutty aroma. This should take about 3-5 minutes. Once browned, remove from heat, transfer to a heatproof bowl, and let it cool for 10 minutes.
In the bowl of a stand mixer, combine the browned butter, light brown sugar, granulated sugar, and vanilla extract. Mix for 30 seconds until everything is well combined.
With the mixer on low, add the eggs one at a time, followed by the flour, cornstarch, baking soda, and salt. Mix until everything is nicely incorporated.
Remove the bowl from the mixer and gently fold in the chocolate chunks or chips with a rubber spatula until evenly distributed.
Line a large baking sheet with wax paper or parchment paper. Use a medium-sized cookie scoop to make 24 even cookie dough balls. Chill for at least 30 minutes, or up to 24 hours.
When you’re ready to bake, preheat the oven to 350°F. Line another cookie sheet with parchment paper or spray it with nonstick cooking spray. Space out the cookie dough balls about 2 inches apart and bake for 9-10 minutes, or until the edges are just set.
Once out of the oven, let the cookies cool for 3 minutes on the sheet before transferring them to a cookie rack to cool completely. Finish them off with a sprinkle of flaky sea salt, and you’re ready to enjoy these delicious treats!