Preheat the oven to 350 degrees F.
Butter and flour three 8-inch round cake pans and line bottoms with parchment.
Cream together the butter and sugar. Add in the eggs, 1 at a time, mixing well after each.
Whisk together the cocoa powder and hot water.
Whisk together the flour, baking soda, baking powder and salt.
Add ⅓ of the dry mixture into the creamed butter/sugar mixture. Mix. Add in ½ of the warm cocoa/water mixture. Mix again. Repeat till all the flour and cocoa are combined.
Divide batter evenly among the cake pans. Bake for 40 to 50 minutes till a toothpick inserted comes out clean.
Cool for 15 minutes, then remove cake from pans. Cool completely. Carefully cut each layer in half. You will have 6 layers. We only used 5 for this cake. Feel free to use all 6 for a taller cake!
For the chocolate crunch: Crush the cookies in a food processor or with a rolling pin till you get a fine crumb. Place into a large bowl.
Add in the Magic Shell Ice Cream Topping and stir to combine.
Line an 8-inch cake pan with parchment paper. If you happen to have multiple 8-inch pans, you can use them all at once to shorten this process.
Spread about 1/4 of the mixture into the bottom of the pan (or divide mixture depending on how many crunch layers you want to end up with). Chill for about 5 minutes in the freezer till firm.
Run a knife along the edge to help release the crunch layer from the pan. Repeat with remaining crunch mixture. Keep the layers in the refrigerator till ready to stack the cake.
For the buttercream: With an electric mixer, cream the butter till smooth and fluffy.
Gradually add in the powder sugar and cocoa powder. Add in vanilla and milk.
Scrape down sides of bowl.
Beat on medium speed for 1 minutes till well mixed.
To assemble the cake, place down first layer of cake. Spread a little bit of the chocolate buttercream over the layer. Press one crunch layer into the chocolate buttercream. Spread just enough buttercream over the crunch layer to cover it. Add the next layer of cake and repeat this process with the rest of the crunch layers, chocolate buttercream, and cake.
Once fully stacked, frost a very thin layer to crumb coat the cake. Chill for about 30 minutes. Finish with a thicker layer of chocolate buttercream. Using a piping bag fitted with a medium to large star tip, decorate the top edge of the cake with more chocolate buttercream. This cake tastes best a bit chilled so the crunch layer stays firm, but still tastes great at room temperature.