In stand mixer, with paddle attachment, combine butter, cream cheese, sugars, egg, and vanilla. Beat for 5 minutes in a stand mixer or 7 with an electric hand mixer
Scrape sides of bowl and slowly add flour, cornstarch, baking soda, and salt while stirring
Add chocolate chips and stir slowly with mixer or fold in by hand
Cover the dough with beeswax or plastic wrap and refrigerate at least 2 hours or up to 5 days before baking
Preheat oven to 350F
Use spoon to scoop out dough and roll into a ball by hand, then flatten on baking sheet
In between batches, make sure to put the dough back in the refrigerator
Bake for 8-9 minutes, or until edges have set and tops are just beginning to set, even if slightly undercooked. Do not bake longer than 10 minutes
Remove from oven and leave on baking sheet for at least 5 minutes
Move cookies to a cooling rack until fully set
Store in an airtight container at room temperature for up to 1 week