Preheat the oven to 350°F. Line a 13x18-inch rimmed baking sheet with parchment paper and set aside.
In a large mixing bowl, beat the softened butter, light brown sugar, and granulated sugar with an electric mixer on medium speed until the mixture is light and fluffy, about 2 minutes.
Scrape the bottom and sides of the bowl. Add the eggs and egg yolks one at a time, beating well after each addition. Add the vanilla extract and mix until fully incorporated.
Add the all-purpose flour, cornstarch, baking soda, and salt to the bowl. Stir gently with a spatula until the dry ingredients are almost combined.
Add the semi-sweet chocolate chips and continue folding the dough until no visible flour streaks remain.
Transfer the cookie dough to the prepared baking sheet. Press the dough evenly into the pan, spreading it to the edges and corners.
Sprinkle additional chocolate chips over the top, if desired. Add a light sprinkle of flaky sea salt, if using.
Bake for 20 to 25 minutes, or until the top is lightly golden brown and the center appears set.
Remove the baking sheet from the oven and allow the cookies to cool in the pan for at least 20 minutes.
Carefully lift the cookie slab from the pan and transfer it to a wire rack to cool completely.
Slice into 24 bars. Serve warm or at room temperature.