In a medium bowl, whisk together the flour, cornstarch, baking soda and salt until combined.  Set aside. Using a separate mixing bowl, either with a stand mixer or a hand mixer, cream together the softened butter and sugars on medium-high speed until the mixture is light and fluffy and a pale yellow color, about 2 minutes, scraping down the sides of the bowl occasionally as needed. Add egg and vanilla, and beat on medium speed until combined, about 30 seconds. Add the dry ingredient mixture, and beat on medium-low speed until just combined. Fold in the chocolate chips by hand, using a spatula or wooden spoon, until they are evenly combined. Transfer the dough to an airtight container and refrigerate it for 2 hours, or until it is chilled through. Heat oven to 350°F.  Line a baking sheet with parchment paper; set aside. Once the cookie dough is completely chilled, remove it from the refrigerator.  Scoop out and roll dough balls that are 1-inch in diameter.  Then place the dough balls on a baking sheet that is covered with either parchment paper or a silicone baking mat. Bake for about 10-12 minutes, or until the edges are slightly crispy and the tops of the cookies are very lightly golden.  The centers may look slightly undercooked. Remove the cookies and let them cool on the baking sheet for about 5 minutes.  Sprinkle with a pinch of flaky sea salt, if you would like.  Then transfer them to a wire rack to finish cooling. Then dive in while the cookies are nice and warm!  Or, transfer to a sealed container and store for up to 3 days, or freeze for up to 3 months.