Boil the mixture of oil, butter, and coke in a saucepan over medium heat. Add flour to the saucepan and remove from the heat. Now, add baking soda, eggs, buttermilk, and vanilla. Mix until all these are incorporated in the batter.

Mix butter with cocoa frosting and add chocolate syrup, coke, and vanilla to the mixture. Add powdered sugar and continue whisking until the required texture is achieved.

Pour this batter into the baking pan and bake it in the preheated oven (350 F) for about 30 minutes. Then, remove it from the oven and keep it aside to cool for a few minutes. Pour the frosting over the cake. Level the frosting and garnish it with ice cream or whipped cream.