Prepare a cookie sheet with parchment. Set to the side.
In a medium-sized bowl, combine the flour, cornstarch, baking soda, and salt. Set to the side.
In a medium-sized bow with a hand mixer or in the bowl of the stand mixer with a paddler attachment, cream the butter with the sugar until light and fluffy, about 2-3 minutes. Scrape down the bowl as needed. Add in the egg plus the egg yolk, followed by the vanilla and mix well. Scrape down the bowl as needed.
Gradually add the flour mixture to the butter mixture, scraping down the bowl as you mix. Mix in the bag of baking chips, making sure they are fully combined.
Form the cookie dough balls using a cookie scoop and place them on the prepared parchment. Chill the cookie dough in the fridge for 1 hour, or overnight.
While the dough is chilling, preheat the oven to 350. After an hour, bake the cookies on the parchment for 10-12 minutes, until the edges of the cookies are set. Let the cookies chill on the cookie sheet for 5 minutes and move to a cooling rack.
