Step 1: Preheat your oven to 350°F (175°C) and line a large baking sheet with parchment paper.
Step 2: In a medium bowl, whisk together the flour, baking soda, baking powder, and kosher salt. Set this dry mixture aside.
Step 3: In a large mixing bowl, combine the melted and cooled unsalted butter, light brown sugar, and granulated sugar. Whisk vigorously for 1-2 minutes until the mixture forms a paste-like consistency.
Step 4: Whisk in the large egg and vanilla extract until the mixture is smooth and well combined.
Step 5: Gradually add the dry ingredients to the wet ingredients. Use a rubber spatula to fold them together until a few streaks of flour remain. Add the semisweet chocolate chips and continue to fold gently until the chocolate chips are evenly dispersed and all flour is blended in. Be careful not to overmix.
Step 6: For large cookies, use a 2oz cookie scoop (or 1/4 measuring cup) to scoop 5 dough balls onto the prepared baking sheet. For regular-sized cookies, scoop 6 dough balls. Bake for 12-15 minutes for large cookies (12 for gooier, 15 for more done) or 10-12 minutes for regular-sized cookies.
Step 7: The cookies are done when they have golden edges but are still pale and slightly puffed in the center. If cookies spread too much, use a fork to gently nudge the sides inwards immediately after removing them from the oven.
Step 8: While the cookies are fresh from the oven, press a few extra chocolate chips onto the tops and sprinkle with flaky sea salt.
Step 9: Transfer the baked cookies to a wire rack to cool. Repeat with the remaining dough.
Step 10: Allow the cookies to cool for at least 20 minutes before serving. They are best enjoyed slightly warm with the chocolate still melty. Enjoy your perfect gooey chocolate chip cookies!