Preheat oven to 350 degrees.  Grease the bottom and sides of a 9 x 13  baking pan with butter then set aside.

In a large bowl, whisk together the flour, white granulated sugar, baking soda, salt, and cinnamon.  Then set aside.

In a saucepan on medium heat, add 1 ½ cups Coca-Cola, and 1 cup butter.  Stir until butter has melted, then add ¼ cup cocoa powder and continue to stir and bring just to a boil.  Then add to the flour mixture and stir until combined.

In a small bowl, whisk together eggs, buttermilk, and vanilla.  Then add to the flour mixture and stir until well blended (the cake batter will be thinner than regular cake batter).

Pour cake batter into buttered 9 x 13 baking pan and bake for 25 to 30 minutes, or until a toothpick inserted in the center of the cake comes out clean.

Start preparing the frosting about 20 minutes before cake has finished baking.  In a saucepan on medium heat, add 1 ½ cups Coca-Cola and bring to a boil.  Turn heat down to low and simmer for about 15 minutes, or until the Coca-Cola has reduced by half.  Then add in ½ cup butter, and ¼ cup cocoa powder, and stir until blended.  Remove from heat.

Then add 4 cups powdered (confectioners) sugar mix and whisk together until well blended and smooth.

Pour warm frosting over warm cake, then set aside to cool for about 1 to 2 hours (do not refrigerate).  Serve with your favorite vanilla ice cream, or just by itself….it is out of this world Delicious!