Preheat your oven to 350°F (175°C). Line a large baking sheet with parchment paper.
In a medium-sized bowl, whisk together the all-purpose flour, baking soda, baking powder, and kosher salt until well combined.
In a separate large mixing bowl, combine the melted butter, light brown sugar, and granulated sugar using a whisk. Whisk vigorously for about 1-2 minutes until you achieve a paste-like consistency before adding in the egg and vanilla extract.
Gradually pour in the dry mixture into your wet ingredients while folding gently with a rubber spatula. Leave some streaks of flour in the dough before adding in the semisweet chocolate chips to prevent overmixing.
Using a large cookie scoop or measuring cup, scoop out portions of dough onto your prepared baking sheet—five per sheet for large cookies or six for regular-sized ones. Bake them in the preheated oven for about 12-15 minutes depending on your desired gooeyness.
Once baked, let your cookies cool on a rack after topping them with extra chocolate chips and flaky sea salt. Allow them to cool slightly before indulging in these heavenly treats!