My mom made this for my birthday back in the 70's. It was my favorite. Moist, chocolaty,fudgy....and did I say MOIST? You want to eat the whole pan, and might find reasons to keep getting a piece....many times in a day!
Bring to a boil the water with the butter and 4 T. cocoa in a small pan, then set aside to cool to just warm.
In a large bowl, mix sugar,flour,cinnamon,salt, eggs, baking soda and buttermilk. Then stir in the boiled mixture above. Pour into a 9x13 greased and floured pan. Bake at 350 degrees for 30 minutes. Durinig the baking time mix up the frosting which is 1 cup of margarine, 4 T. of cocoa powder, 1 box of powdered sugar and 1 T vanilla. 1 cup of chopped nuts is optional.
While the baked cake is still very warm take a toothpick and poke holes all over the cake. Then pour over the frosting and smooth out. It will slighty melt into the cake but it adds to the moistness. Let cool, cut and serve.