Preheat oven to 325 degrees. Spray the bottom and sides of three 8-inch cake pans with cooking spray and line bottoms with parchment. Spray again. Set aside.

In the bowl of a stand mixer, combine the flour, sugar, cocoa powder, baking soda, baking powder, and salt. Stir to combine.

In a different, medium sized bowl, combine the eggs, buttermilk, water, oil and vanilla. Whisk to combine.

With the mixer on low speed, gradually add the wet ingredients to the dry ingredients and mix until smooth, about 30 seconds. Scrape down the sides of the bowl and mix again for another 10 to 20 seconds. Divide batter equally among the three cake pans (about 30 ounces of batter in each 8-inch pan).

Bake the layers for about 45 to 50 minutes (time may vary depending on your oven) or until a wooden pick inserted into the center of the cake comes out with only a few moist crumbs on it. Let the cakes cool in pans on a wire rack for 10 to 15 minutes, and then turn onto a rack to cool completely. When completely cooled, you can cut the cakes in half. See video above.

Wrap the layers in plastic wrap and chill for at least an hour in the freezer. Cakes can be made a week ahead of time and wrapped in plastic wrap. If you'd like to store the cake layers longer than a week, wrap in tin foil, as well, and then place in a zip lock bag.

In the bowl of a stand mixer fitted with the whisk attachment, whisk the heavy whipping cream on high for about 3 to 5 minutes, until the cream forms stiff peaks. Transfer the cream to another bowl and set aside.

In the now empty bowl of a stand mixer fitted with the paddle attachment, beat the cream cheese for a couple minutes until smooth. Gradually add the powdered sugar. Beat for a couple minutes until smooth.

Fold in the whipped cream until no streaks of whipping cream remain.

*If you are making this ahead of time, don't add the Oreos yet. Instead cover and store the filling (without the Oreos) in the fridge until you're ready to stack the cake.

When you're ready to stack the cake, fold in the Oreos.

In a food processor or blender, pulverize the Oreos to a find crumb. You do not need to remove the cream filling. Set aside.

In the bowl of electric mixer fitted with the paddle attachment, combine the butter and peanut butter. Beat on medium-high speed until smooth, about 2 to 3 minutes.

Add the powdered sugar to the bowl and mix in, slowly at first until incorporated, then increasing the mixer speed to high once all of the powdered sugar has been added. Blend in the vanilla extract, salt and heavy whipping cream, and continue to whip on high speed until very fluffy, about 4-5 minutes, scraping down the sides of the bowl as needed.

Stir by hand with a wooden spoon to push out air pockets.

Remove and reserve two cups of the buttercream for the cake layers. Add the crushed Oreos to the remaining buttercream and stir well.

Heat 3/4 cup cream in a microwave safe bowl. Pour the cream over the chocolate chips and let sit for 5 minutes. Once the chips are heated from the cream, stir until the cream and the chips make a smooth and silky consistency.

If the drip feels too thick at this point, heat another 1/4 cup heavy cream and add it to the mixture.

Place the first cake layer top side up, in the center of the cake board. (I find that using a cake lifter helps move the thinner cake layers around. See above video).

Pipe a rim of Oreo buttercream around the edge of the cake and then fill the center with about 1 cup of the Oreo cream filling. 

Place the second cake layer on top of the filling and evenly spread one cup of the buttercream over the cake layer.

Repeat these steps with the remaining layers. The fillings should be: Oreo cream, peanut butter, Oreo cream, peanut buttercream and Oreo cream.

Place the final cake layer, top side down, on the final layer of Oreo cream filling.

Cover the cake in a thin layer of the Oreo buttercream. This will be your crumb coat. If you find that your cake is not stable, add a few plastic straws down the center of the cake to act as support dowels. Once your crumb coat is complete, freeze the cake for about 15 minutes.

Once the crumb coat is set, continue to frost the cake and use your drip and any extra buttercream for piping.