Preheat oven to 375 °F. Line a baking sheet with parchment paper or a baking mat, set aside.
In the bowl of a stand mixer fitted with a paddle attachment cream butter and sugars on medium speed for 2-3 minutes. Add eggs and vanilla and mix until combined. Scrape down the sides of the bowl as needed. Add flour, cocoa, 1 cup of Oreo crumbs, baking soda, and salt. Mix to combine.
Portion into 1/3 cup balls. Roll each ball in the remaining 1 cup of crushed Oreos. Place the Oreo covered balls on a parchment lined baking sheet. (6 per pan). Use the palm of your hand to press down on the cookie just slightly.
Bake for 9-11 minutes or until the tops no longer appear shiny. Remove from oven and let cookies cool on pan for 10 minutes then transfer to wire rack to cool completely.
Make the mallow filling: In a medium bowl beat the butter, vanilla, and powdered sugar until fully combined. Mix in the marshmallow fluff and crushed Oreos by hand with a rubber spatula.
Scoop 2 T of mallow fluff onto one side of an Oreo cookie, then sandwich another cookie on top. You don’t want to overfill will the cream filling otherwise it will ooze out. You can chill the cream for 10 minutes to make it easier to scoop if you’d like. (I use a cookie scoop to portion the cream onto each Oreo sandwich cookie). Enjoy!