• Preheat your oven to 350 degrees F. and prepare 3 6-inch or 2 8-inch cake pans by rubbing generously with vegetable shortening and dust with flour.
• In the bowl of a stand mixer equipped with a whisk attachment, add the flour, sugar, baking powder, and salt. Whisk until combined.
• With the mixer on low speed, add the butter in 1 tablespoon at a time. Mix until you have a dry sand- like consistency.
• Add in the vegetable oil, sour cream, vanilla, and milk and whisk until combined and smooth.
• Add the egg whites in last and mix until the whites are just mixed into the batter.
• Fold in the Oreo pieces last.
• Divide the batter evenly between the cake pans. If you want to be precise, measure the batter and divide by 3. (Or 2 if you are using 8-inch pans)
• Bake for 35-40 minutes checking around the 30-minute mark for doneness. The cakes are done when you can insert a toothpick into the thickest part of the cake and the toothpick comes out clean.
• Remove from the oven and allow the cakes to cool about 10 minutes in the pan, then invert onto a wire rack to cool completely,

Frosting:

• While the cakes are cooling, prepare the frosting by adding the butter into the bowl of a stand mixer equipped with a paddle attachment and cream for 3-4 minutes until smooth.
• Add the powdered sugar, one cup at a time, incorporating after each addition.
• Next, add in the heavy whipping cream and mix on low speed. Slowly increase the speed to high for 5-6 minutes. The buttercream will become light and fluffy.
• Fold in the crushed Oreos last.
• Add the frosting to a large piping bag with a large round tip

Assembly:

• Make sure the cake layers are level by cutting off the domes using a serrated knife or a cake level.
• Place one cake layer face down on a cake server or plate and top with about 1/3 of the frosting and smooth.
• Continue with each cake layer. Once all layers are stacked, smooth the remaining buttercream over the outside of the cake and smooth with an offset spatula or cake frosting smoother. Place the cake in the refrigerator while you prepare the ganache.
• Add the chocolate and heavy whipping cream into a microwave safe bowl and microwave on 30 second increments until melted and smooth.
• Allow to cool for about 5 minutes, then add to a condiment bottle or just use a spoon to smooth the ganache over the top of the cake, allowing some drips to come off the sides.
• Pipe some whipped cream around the border of the cake and sprinkle with crushed Oreos and serve!
• Keep covered in an airtight container and store in the refrigerator for up to 4 days.