Preheat the oven to 350 degrees.  Line a few baking sheets with parchment and set aside.

Using a food processor, crush the Oreos into fine crumbs.

In a medium bowl, combine the crushed Oreos, flour, corn starch, baking soda, baking powder, cocoa, cream of tartar and salt.  Mix well.  Set aside.

In the bowl of a stand mixer, combine the softened butter and sugars.  Cream until smooth.

Add in the oil and egg.  Mix well.

Add in the bowl of dry ingredients and mix thoroughly, scraping the sides often.

Using a large ice cream scoop, divide the cookies between the prepared baking sheets.

Gently flatten into a disc shape.  Bake in the preheated oven for approximately 10 minutes or until the centers are set.  Allow to cool completely before decorating.

In the bowl of a stand mixer, combine the softened butter, powdered sugar, vanilla and salt.  Mix on low until combined.  Scrape down the sides and then bump up the speed to medium for about a minute or until the frosting is smooth and creamy looking.

Spread a layer of frosting over the top of each cookie.

Sprinkle with additional Oreo crumbs to decorate.