Preheat your oven to 375°F and line a baking sheet with parchment paper or a silicone baking mat.
In a medium bowl, whisk together the all-purpose flour, cornstarch, baking powder, baking soda, and salt until well combined.
In another bowl, cream together the room-temperature unsalted butter, packed brown sugar, and granulated sugar using a mixer on medium speed for about 2-3 minutes.
Add in the large egg and vanilla extract to your butter-sugar mixture and beat on medium speed for about one minute until fully incorporated.
Gradually mix in your dry ingredients until JUST combined; gently fold in the Guittard baking chips.
Using a ½ cup measuring cup or kitchen scale, portion out equal-sized balls of dough onto your prepared baking sheet.