Preheat your oven to 350°F (175°C). Grease and flour a 13 x 9-inch baking pan.
In a saucepan, combine Coca Cola, oil, butter, and cocoa. Bring the mixture to a boil, ensuring the butter melts completely and the cocoa is fully dissolved.
In a large mixing bowl, whisk together the sugar, flour, and salt.
Pour the boiling Coca Cola mixture over the dry ingredients and mix until well combined.
Add eggs, buttermilk, baking soda, and vanilla to the mixture and beat well until smooth.
Pour the batter into the prepared baking pan.
Bake for 20 to 25 minutes, or until a toothpick inserted into the center comes out clean.
Let the cake cool for about 10 minutes before frosting.
For the frosting, combine butter, cocoa, and milk in a saucepan and heat until the butter melts. Remove from heat and gradually beat in confectioner's sugar and vanilla until smooth.
Spread the frosting over the cake while it's still warm. Allow it to set before slicing and serving.
