Preheat the oven to 375F degrees
In a small bowl, combine dry ingredients - flour, cornstarch, salt, baking soda, and baking powder. Mix with a fork or whisk to combine.
In the bowl of a stand mixer, place butter and both sugars. Mix, using a paddle attachment cream for 3 minutes until light and fluffy. Scrape the sides of the bowl with a nonstick spatula
Add in egg, egg yolk, and vanilla. Mix again until combined. Make sure to scrape the sides of the bowl again so that the dough is mixed evenly
In a small separate bowl, combine all dry ingredients except the Oreos and chocolate.
Add dry ingredients to stand mixer and mix dough until combined.
Add in oreos and chocolate. Dough will be very thick!
Scoop dough into 4 oz balls.
On a parchment-lined baking sheet, place 4 dough balls at a time.
Bake for 8-10 minutes until sides are set. Cookies will be undercooked on the inside!
