1. First, preheat the oven to 375°. Grease and lightly flour a 9X13 baking cake pan.
2. Next, sift flour and sugar together in a large mixing bowl.  A short cut that I use, if I do not want to get the sifter out, is to use a wire whisk to blend the two.
3. Then, place the stick of butter, cocoa, water, and oil in a medium sauce pan.  Bring this mixture to a boil.
4. Now, add the boiled mixture to the flour and sugar.  Blend  these until combined.  Next, add the eggs, buttermilk, baking soda, cinnamon, and vanilla. Batter should be smooth and creamy.
5. Pour the batter into the greased and floured cake pan.  Bake 20-25 minutes, if using a 9X13 cake pan and 15-20 minutes if using the sheet cake pan.
6. Once the cake is done, allow it to cool while you make the icing.

For the Icing

1. Put one stick of butter into a medium sauce pan.
2. Then add 2 heaping tablespoons cocoa, through a fine mesh sieve into the pot. This step is not critical but it will prevent any clumps of cocoa powder from forming in the icing.
3. Next, add about 6 tablespoons buttermilk (or regular milk) to the pot and bring to a rolling boil in a medium sauce pan.
4. Once it reaches the rolling boil, remove the pan from the heat.
5. Into the pot, add about 1 lb powdered sugar.  I use a fine mesh strainer/ sieve to sift reduce any clumps in the sugar as I add it into the chocolate.
6. Then add vanilla last and blend well.
7. Finally, pour the warm frosting onto the cake evenly.  It will harden into a velvety icing as it cools.