For the Cake

1. Preheat the oven to 350°F.
2. Coat 2 8- inch round cake pans with nonstick spray and line the bottoms with parchment rounds. Coat the parchment paper in nonstick spray and set the pans aside. 
3. In the bowl of your stand mixer fitted with the paddle attachment mix the butter and sugars together for 2 minutes on medium-high speed, until light and fluffy. Add in the eggs one at a time and then add vanilla. Mix well, scraping the sides of the bowl as necessary.
4. In a separate bowl, sift together the flour, cocoa powder, baking soda, and salt. Set aside. In another bowl, whisk together the buttermilk, coffee and sour cream.
5. On low speed, add in alternating additions the flour mixture and the milk mixture, beginning and ending with the flour mixture.  Scrape down sides when necessary. Mix until just incorporated.
6. Bake for 20-25 minutes, until center is set.
7. Cool the cakes in the pans for 10 minutes, then remove cakes from pans and transfer to a wire rack to cool completely. 

For the Buttercream

1. On medium-high speed in the bowl of your stand mixer, mix the butter and shortening together for 2 minutes until smooth.
2. Slowly add in the powdered sugar, scraping the sides when necessary.
3. Add the cream and vanilla and beat at medium speed until it reaches the consistency you like, adding more cream if you’d prefer.
4. Set aside 2 cups of plain buttercream. Now on low speed, combine the crushed Oreos with the frosting until they are mixed in thoroughly.

To Assemble

1. When the cake layers are completely cooled, cut each in half to make 4 layers. Layer the cake with the Oreo buttercream.
2. Once layered, use the reserved vanilla buttercream to frost the outside of the cake. Decorate as you like!