Preheat oven to 350F and grease cake pans.
In a stand mixer, fitted with the paddle attachment, combine the flour, sugar, cocoa, baking soda, baking powder, salt and mix until combined. Add the two eggs and mix. While the mixer is beating, slowly add the buttermilk, oil and vanilla. Ensure that water is hot, and add water slowly. Once batter is combined, add quartered Oreo’s and mix a couple of times, being careful not to break up the Oreo’s. Divide the batter into two equal portions in prepared cake pans and bake for 40-45 minutes or until a toothpick inserted comes out clean. Allow to sit on a cooling rack before removing from pan and allow to cool completely.
In a stand mixer, fitted with the paddle attachment, combine flour, sugar, baking powder and salt and mix until combined. While mixer is turning, add cubes of butter one at a time and mix until the butter has broken up into tiny pieces and the mixture resembles sand. Add eggs and continue to mix. While mixer is turning, slowly add milk and vanilla. Mix until batter is smooth. Pour batter into prepared cake pan and bake for 40-45 minutes or until a toothpick inserted comes out clean. Allow to sit on a cooling rack before removing from pan and allow to cool completely.
While cakes are cooling, prepare filling. In a stand mixer, fitted with the whisk attachment, whisk whipping cream until stiff peaks form. Set aside in the fridge. Switching to a paddle attachment in a clean bowl, beat cream cheese until cream cheese is soft. Add icing sugar and vanilla and mix until smooth. Add whipped cream to cream cheese mixture, and mix until smooth.
Ensure that each cake layer is even and level. Place one chocolate cake on a cake board and smooth about 1/2 cup of filling onto it in an even layer. Place the vanilla cake layer on next and repeat with a 1/2 cup of filling. Smooth the filling on top. Place the second chocolate cake on top, and cover the entire cake in a layer of filling. At this point, I always like to place in the freezer for about 20-30 minutes (to set the cake). Apply a second coat to the cake with the filling. Place remaining filling into a piping bag fitted with a large open star tip (I used Ateco 827) and place in the fridge for later.
Prepare chocolate ganache and pour onto the edge of cake, a small amount at a time. Place some crumbled Oreos in the centre of the cake, and using remaining filling, pipe large open stars in a circle. Place a half Oreo on top of every second star. Slice and serve!