In a medium bowl, stir together the flour, cornstarch, baking soda, and salt and set aside.
In a large bowl, using an electric mixer fitted with a paddle or whisk attachment, cream the butter, granulated sugar, and brown sugar on medium-high speed for 2-3 minutes. Then add the egg and vanilla and mix for about 1 minute, until creamy and well combined.
Add the flour mixture and mix on medium-low speed just until incorporated, about 30-60 seconds. Then add the chocolate chips and mix on medium-low speed just for a few seconds until well distributed. Then cover and chill for 1 hour.
Line 2-3 baking sheets and preheat the oven to 350°F (175°C).
Scoop 16 equal-sized balls (about 2 tablespoons [45g]) of chilled cookie dough and roll into balls. Place 6-8 cookies, spaced 4 inches (10cm) apart, on each prepared baking sheet. Bake one sheet at a time for 10-11 minutes, or until the edges of cookies are set and lightly browned, and the center looks undone, pale, dry, and lightly puffed.
Remove from the oven and let cool on the baking sheet for about 5 minutes, or until firm enough to move. Then, transfer to a wire rack and let cool completely. The cookies will stay fresh in an airtight container at room temperature for up to 4 days or freeze for up to 3 months.