Step 1: Preheat your oven to 350°F (175°C) and grease two 8-inch round cake pans with butter and a dusting of cocoa powder.
Step 2: In a large bowl, sift together the flour, sugar, cocoa powder, baking soda, baking powder, and salt.
Step 3: Add the buttermilk, vegetable oil, eggs, and vanilla extract to the dry ingredients and whisk until well combined.
Step 4: Carefully stir in the hot water (or coffee) by hand. The batter will be thin, which is normal for this oreo cake recipe.
Step 5: Gently fold in the 15 coarsely crushed Oreo cookies into the batter.
Step 6: Divide the batter evenly between the two prepared pans and bake for 30-35 minutes, or until a toothpick comes out clean.
Step 7: Allow the cakes to cool in the pans for 10 minutes before transferring them to a wire rack to cool completely.
Step 8: For the frosting, beat the softened butter for 5 minutes until light. Gradually add powdered sugar, Oreo crumbs, and heavy cream, beating until smooth.
Step 9: Frost the cooled cake layers, adding extra crushed cookies between layers and decorating the top with whole Oreos.