Preheat the oven to 400°
In a large bowl, sift together flour, cornstarch, baking powder, baking soda, and salt.
In a separate bowl, with a whisk or electric hand mixer, beat the butter and sugars together until fluffy. Add in egg and egg yolk and still until combined
Slowly add in flour mix, combining with a rubber or wooden spoon. Add in chocolate chips and stir until combined.
Using a large spoon or small ice cream scoop, form dough into balls, about the side of a golf ball. Place on a baking tray lined with parchment paper, about 2 inches apart (they will spread.
Back for 10-12 minutes our until slightly browned on the top. Remove from oven and allow to cool on baking sheet for 5 minutes. Then move to a cooling rack to cool completely.
Serve while warm or store in an airtight container.
