Preheat oven to 350 degrees Fahrenheit. Grease a 9x13” baking pan with cooking spray. Line with parchment paper if you’d like.
For the cake, put flour, sugar, cocoa, baking powder, baking soda and salt in a bowl and whisk well.
In a stand mixer, mix the buttermilk, oil, eggs, vanilla together. Slowly add in the mix of dry ingredients while the mixer is on low. Add the coffee and make sure everything is combined. The batter will be very thin.
Pour the batter into the prepared pan and bake for about 30-35 minutes or until a toothpick inserted in the middle comes out clean.
Allow the cake to cool on a wire rack. After it is mostly cooled, place it in the freezer to so the topping is easier to apply. Try to let it freeze for at least 20 minutes.
Make the buttercream:
In a stand mixer using the whisk attachment, cream the butter, shortening and vanilla for 2-3 minutes until it is almost white in appearance.
Add the powdered sugar 1 cup at a time, while mixing on low speed. Cover the mixer with a dish towel, if needed, to prevent powdered sugar from blowing out of the bowl.
Add in the heavy cream a tablespoon at a time, and continue mixing on low. Add more cream as needed to get the desired consistency.
Place the frosting in a decorating bag with a large open circle tip. (Wilton 1A or slightly smaller. This will depend on how tall you want your bumps.)
Pipe 4 frosting ribbons across the cake evenly (they should be about 1-inch wide). Place the cake back in the freezer while you make the fudge frosting.
Make the fudge frosting:
In a medium saucepan over medium low heat, combine the buttermilk, sugar, corn syrup, cocoa powder, salt and half of the butter. Bring the mixture to a boil and heat to the soft-ball stage (234-240 degrees Fahrenheit).
Remove from heat and add the remaining butter cubes. Stir until melted.
Whisk in the powdered sugar and vanilla extract until well combined.
Remove the cake from the freezer and drizzle the fudge frosting over the cake evenly. If the fudge starts to harden, you can rewarm it to melt it again.
Put the cake in the freezer for 15 minutes to set.
Store in an airtight container. Any leftovers can be stored at room temperature for up to 3 days or in the refrigerator for up to 5 days.
The calories shown are based on the cake being cut into 15 pieces, with 1 serving being 1 slice of cake. Since different brands of ingredients have different nutritional information, the calories shown are just an estimate. **We are not dietitians and recommend you seek a nutritionist for exact nutritional information. The information in the nutrition box are calculated through a program and there is room for error. If you need an accurate count, I recommend running the ingredients through your favorite nutrition calculator.**