For the Cake: 

1. Preheat the oven to 350°F. Prepare three 8-inch round baking pans, line the bottom with parchment paper, and grease the sides. Prepare bake even stripes if desired.
2. In a large mixing bowl, combine the sugar, vegetable oil, eggs, and vanilla extract. Beat on medium speed until well incorporated. Scrape down the bowl as needed. Next mix in the sour cream and beat until well combined.
3. In a separate bowl combine the remaining dry ingredients and sift together the flour, baking powder, and salt. Add half the dry ingredients, and half the milk, and beat on low speed just until the flour starts to incorporate. Repeat until all ingredients are added and combined. Use a spatula to scrape down the sides of the bowl and stir the batter from the bottom to the top to ensure it’s well mixed.
4. In a large Ziploc bag, crushed the Oreos into small pieces using a rolling pin or something similar. Fold the crushed Oreos into the cake batter.
5. Divide the batter evenly between the three pans, about 1 3/4 cups of batter per pan. Bake at 350°F for 20-25 minutes. Test the cake for doneness by inserting a toothpick into the center of the cake. If the toothpick comes out clean, the cake is done. Remove from the oven and allow to cool completely.

For the Chocolate Fudge Frosting: 

1. In a microwave-safe bowl, melt the chocolate in the microwave at 50% power in 30-second increments, stirring each time until the chocolate is melted. Stir until completely smooth. Set aside to cool.
2. Cut the butter into 1 tablespoon size pieces. Using the paddle attachment, whip butter for 3-4 minutes, scraping down the bowl occasionally. Beat until the butter in whipped and airy. Next, beat the cocoa powder into the butter until well-mixed, scrape down the sides of the bowl as needed.
3. Alternate adding 1 cup of powdered sugar at a time with the liquid ingredients: vanilla extract & heavy cream. Ensure the powdered sugar is well combined, and whip for 1-2 minutes before adding more powdered sugar.
4. Next, pour in the melted chocolate and beat on slow speed until incorporated. Then, increase the speed to medium-high and beat for another 2-3 minutes to whip additional air into the frosting. Once ready, place the frosting in a large piping bag and set aside. 

For the Oreo Frosting

1. Cut the butter into 1 tablespoon size pieces. Using the paddle attachment, whip butter for 3-4 minutes, scraping down the bowl occasionally. Beat until the butter is whipped and airy.
2. Alternate adding 2 cups of powdered sugar at a time with the liquid ingredients: vanilla extract & heavy cream. Ensure the powdered sugar is well combined, then whip for 1-2 minutes before adding more powdered sugar.
3. In a food processor, grind the Oreos into fine crumbs then add to the frosting and slowly beat the crumbs into the frosting then beat at a high speed for 60 seconds.
4. Place the frosting in a large piping bag (about ¾ full) fitted with a piping tip 789. If you don’t have one, use a large open round tip.

To Assemble

1. Use a cake leveler or serrated knife to cut the domes off the top of the cake. Place a dollop of frosting on the cake board and place the bottom layer of cake on top of that.
2. Pipe the first layer of chocolate frosting. Snip the end of the piping bag off and pipe the filling working in circles from the outside edge to the middle. Spread evenly with an offset spatula. Add the second layer of cake and add the remaining chocolate frosting. Place the third layer of cake on top. Use an offset spatula to remove any excess chocolate frosting from the edges of the cake.
3. Next, use an offset spatula to frost a light crumb coat of Oreo frosting on the outside of the cake. To finish, pipe the Oreo frosting along the outside edge of the cake, then use an offset spatula or icing smoother to create a smooth edge. Using your hands, gently pack the Oreo crumbs along the bottom of the cake. Once completed, refrigerate for 30 minutes.

For the Chocolate Ganache:

1. In a microwave-safe bowl, combine the chocolate and the heavy whipping cream. Melt the chocolate in the microwave at 50% power in 30-second increments. Once the chocolate is fully melted and stirred smooth, add the corn syrup and stir the mixture until it’s well mixed. Cool the ganache in the refrigerator for about 10 minutes before pouring over the cake.
2. Allow the ganache to set for 20-30 minutes at room temperature. Garnish with remaining Oreo frosting and Oreo cookies.