Follow these steps to create your own layered masterpiece:

1. Preheat your oven to 350°F and grease three 9-inch round cake pans.
2. In a medium bowl, whisk together the flour, cocoa powder, baking powder, baking soda, and salt.
3. In a large bowl, cream together the softened butter and granulated sugar until light and fluffy, about 3 minutes.
4. Add eggs one at a time, beating well after each addition, then mix in the vanilla extract.
5. Alternately add the dry ingredients and buttermilk to the butter mixture, starting and ending with the dry ingredients.
6. Divide the batter evenly among the prepared pans and smooth the tops with a spatula.
7. Bake for 18-20 minutes, or until a toothpick inserted into the center comes out clean.
8. Let the cakes cool in the pans for 10 minutes, then turn them out onto wire racks to cool completely.
9. For the frosting, whip the heavy cream until soft peaks form. Add powdered sugar and vanilla extract, and continue whipping until stiff peaks form.
10. Fold in the crushed chocolate sandwich cookies into the whipped cream mixture.
11. To assemble, place one cake layer on a serving plate and spread with a generous layer of cookies-and-cream frosting. Repeat with remaining layers and frosting.
12. Finish the cake by frosting the top and sides, then garnish with extra crushed cookies if desired.