Preheat oven to 350 degrees. Line a cookie sheet with parchment paper or Silpat mat. Set cookie sheet aside.
In a mixing bowl beat the butter and sugars on medium speed for several minutes until mixture becomes light and fluffy
Turn mixer to low and beat in the eggs and vanilla. Stop mixer, scrape bowl, then turn mixer to low speed and slowly add in the flour, cornstarch, baking powder, baking soda, and salt, stirring until mixture is combined. Fold in the chocolate chips. (Note: for a truly authentic Crumbl cookie you must use Guittard chips like the bakkery does.)
Take ¼ cup of cookie dough (5.5 ounces of dough if using a scale) and form into a ball, then place on cookie sheet leaving several inches of space for cookies to spread. Bake at 350 degrees for 15-20 minutes, or until cookies are lightly browned and edges are cooked.
Remove cookies from oven and allow them to cool for several minutes on the cookie sheet before moving to a cooling rack to finish cooling completely. But we highly suggest eating these cookies warm from the oven.
Notes
Store cookies in an airtight container for up to one week or in the freezer for up to one month.For best results, chill dough for 30 minutes prior to baking.