Preheat oven to 350°F. Line two baking sheets with parchment paper or a silicone mat.
In a medium bowl, whisk together the flour, baking soda, salt, and cornstarch (if using).
In a stand mixer or large bowl, beat the softened butter, brown sugar, and granulated sugar until light and fluffy—about 5 minutes.
Add the egg and vanilla extract, beating until well combined.
Gradually add the dry ingredients to the wet mixture, beating just until combined.
Gently stir in the chocolate chips by hand to avoid over-mixing.
Scoop the dough into 1½-tablespoon balls and place them on the prepared baking sheets.
Press a few extra chocolate chips on top of each ball for extra gooey centers.
Bake for 12 to 14 minutes, or until the edges are golden brown.
Let the cookies cool on the pan for 5-10 minutes before transferring to a wire rack.
Sprinkle with flaky sea salt for a bakery-style touch.