Preheat oven to 375 degrees Fahrenheit.
Cream the butter and brown sugar together.
Add the eggs and vanilla extract and mix well.
In a separate bowl, combine the flour, cornstarch, baking powder, and salt.
Crush the Oreo cookies and add them to the flour mixture.
Add a splash of milk to the flour mixture to loosen up the whites.
Fold the dry ingredients into the wet ingredients until just combined.
Scoop the dough into a jar or container and bake until fully cooked.
Allow the cookies to cool completely before stacking.
