Make the cake layers: Preheat oven to 350 degrees.
Line three 9-inch cake pans with baking spray and parchment. Prepare peanut butter cookies, brownies and chocolate chip cookies according to box instructions. Pour each into a cake pan and bake according to box instructions. Set aside to cool.
Make the Oreo frosting: In a large bowl, mix frosting and Oreo crumbles until combined. Set aside.
Assemble the cake: Place peanut butter cookie layer on a cake stand. Spread 1 cup Oreo frosting evenly across the top and then cover with the brownie layer. Spread another layer of Oreo frosting evenly across the top and cover with the chocolate chip layer.
Cover the entire cake with a thin layer of white frosting. Place in refrigerator for up to one hour to set.
Prepare the ganache: Heat heavy cream and pour over dark chocolate. Stir until chocolate is melted.
Pour ganache over the top of the cake to drip down the sides. Top with brownie bites, Oreos and chocolate chip cookies. Cake will keep up to 5 days covered.