Preheat oven to 350°F. Generously grease a 9 ½ inch pie dish and line the bottom with a round of parchment paper. Set aside.
With a hand mixer or stand mixer, beat butter and sugars for several minutes, until light and fluffy. Add egg and vanilla extract, beat to combine, scraping the sides of the bowl as necessary.
In a separate bowl, combine flour, cornstarch, baking soda, and salt. With the mixer on low, slowly add the the dry ingredients, mixing until combined. Be sure to mix in the dry ingredients for at least a full minute.
Using a rubber spatula or wooden spoon, stir in all but 1 tablespoon chocolate chips. Press the dough evenly into the prepared dish (dampen your fingers with water, if necessary). Sprinkle the remaining 1 tablespoon of chocolate chips onto the top of the dough, lightly pressing them down.
Bake for 23-25 minutes, until the edges are light golden brown., and the center is still slightly underdone. Cool completely.