Preheat your oven to 350°F (175°C). Line two large baking sheets with parchment paper and set a wire cooling rack aside.

In a large mixing bowl, combine the melted butter, brown sugar, and granulated sugar. Whisk vigorously for 1 minute until it resembles wet sand. Add the egg and vanilla extract, whisking until the mixture becomes pale and falls in glossy ribbons.

Sprinkle the all-purpose flour, baking soda, and kosher salt over the wet mixture. Use a rubber spatula to gently fold the ingredients together until just combined. Do not overmix.

Fold in the semi-sweet chocolate chips, reserving a small handful to press into the tops of the dough balls later.

Using a 2-tablespoon cookie scoop, portion the dough onto the prepared baking sheets, leaving 2 inches of space between each. Press a few of the reserved chocolate chips into the top of each dough ball.

Bake for 10-12 minutes. The cookies are done when the edges have a golden brown, crispy texture, but the centers still look pale and slightly underbaked.

Remove from the oven and immediately sprinkle the tops with coarse flaky sea salt. Let the cookies rest on the baking sheet for 5 minutes before transferring them to the wire cooling rack to cool completely.