Preheat your oven to 350 degrees.

Grease and flour an 11x17 inch pan or roasting pan.  I did use a Pyrex 4.8 Quart pan next time I will leave some of the batter out as it still overflowed a bit. 

Combine the flour, cocoa powder, cinnamon, salt, baking soda, and sugar in a mixing bowl, and set aside.

In a pan on the stove at low heat, heat the butter with the cups of Coca-Cola until the butter has melted.

Next add eggs, vanilla, and buttermilk to the butter and butter mixture and mix well. 

Add the Coca-Cola liquid mixture into the dry ingredients and beat until mixed well. 

Pour batter into the baking pan and bake for 30 minutes. (You could make 2 tube pans baked for 60 minutes or 24 cupcakes baked for 15 minutes.) 

In a saucepan, heat together the butter and Coca-Cola. Be sure not to boil.

Add in the remaining ingredients and mix well.

Pour icing over the cake. You must ice this cake warm!