Preheat your oven to 350ºF and spray a 9x13 baking pan with cooking spray. Set aside.
In a bowl of a stand-mixer combine the sugar and flour and set aside.
In a saucepan add the Coca-Cola, oil, butter and cocoa powder and stir to combine. Bring to a boil and remove from heat. Add to the flour mixture and combine on medium-low until light, about 1 minute.
Add in eggs, buttermilk, baking soda and vanilla extract and beat until combined. Pour batter into the prepared pan and bake until a toothpick inserted comes out clean, about 30 minutes. Remove from oven and begin preparing the frosting.
For the Frosting
In a saucepan over medium heat combine the butter, cocoa powder and milk to just about boiling. Remove from heat and whisk in powdered sugar and vanilla. Pour over the warm cake and spread with a spatula.
Let cake cook completely to room temperature, then chill for one hour in the fridge. Serve.
Notes
The cake is different than most because it doesn't use a creaming method.Bring the mixture just to a boil when making the frosting.
Perfect Pairing
It's not a meal at Cracker Barrel without fried apples.[embed_recipe id='16699']