Preheat oven to 375°F. Line 2 baking sheets with parchment paper or a silicone baking mat.
In a medium bowl whisk the flour, cornstarch, baking powder, baking soda, and salt; set aside.
Using a mixer, cream the cold-cubed butter, brown sugar, and granulated sugar on medium speed for 3-4 minutes.
Add the egg and vanilla and beat on medium speed for 1 minute.
Add in the dry ingredients and mix until just combined.
Stir in the chocolate chips.
Using a ⅓ or ½ measuring cup, portion the dough into equal ⅓ or ½ cup size dough balls (4-5 ounces each). (I took a ¼ cookie scoop and put two cookie dough scoops together and rolled them in balls. Add more chocolate chips on top, if desired.)
Place 4-6 cookie dough balls on the prepared baking sheet, leaving enough space between each cookie to bake evenly.
Bake cookies for 9-12 minutes. Baked cookies should appear lightly golden with tops set, not wet.
Allow the cookies to cool on your cookie sheets for 10 minutes before transferring them to a wire rack. The cookies need time to set while they are cooling.