Preheat your oven to 350°F (175°C) and grease two 9-inch round cake pans.
In a large bowl, combine flour, sugar, cocoa powder, baking soda, and salt.
In another bowl, whisk together buttermilk, oil, eggs, and vanilla extract.
Gradually mix the wet ingredients into the dry ingredients until smooth.
Fold in the crushed Oreo cookies.
Divide the batter evenly between the prepared pans.
Bake for 25 minutes or until a toothpick comes out clean.
Allow cakes to cool in pans for 10 minutes, then transfer to wire racks.
Whip heavy cream with powdered sugar until stiff peaks form, then frost the cooled cakes.
Decorate with whole Oreos on top.