Preheat oven to 350 degrees F. Spray a 9 X 13 inch pan with nonstick cooking spray.
In a bowl, stir the first 4 ingredients together.
Add the Coca Cola, cocoa, and butter to a saucepan and bring just to a boil. Pour into flour mixture and stir until blended.
Whisk eggs, buttermilk, and vanilla together then add into flour mixture.
Pour batter into baking pan and bake 25-30 minutes or until a toothpick inserted into the center of cake comes out clean.
Meanwhile, make the glaze the last 15 minutes the cake is baking. In a pan, bring the soda to a boil; cook 12-15 minutes or until soda has been reduce to 1/2 a cup. Add the butter, and cocoa and cook until the butter has melted. Remove from heat, add vanilla and Confectioners' Sugar and mix until smooth. Pour immediately over hot cake.
Glaze
Pour the Coca Cola into a saucepan and simmer until the soda has been reduced to just ½ a cup.
Add butter and cocoa. Once the butter has melted, remove your saucepan from the heat and stir in vanilla and sifted confectioners’ sugar.
Pour the glaze immediately over the hot cake once it’s out of the oven.