Place water, butter and cocoa in a saucepan and bring to a boil.
In a mixing bowl, combine sugar, flour and baking soda, mixing well.
Pour first mixture into second mixture.
After mixing well, add eggs, buttermilk and vanilla.
Mix well and spread in oblong Pyrex dish.
Bake at 350 for 25-45 minutes (I bake mine 25 minutes).
About 5 minutes before cake is done, melt butter in a pan.
Add sweet milk and cocoa and bring to a boil.
Remove from heat and pour over powdered sugar, vanilla and pecans.
Beat well and pour over cake while cake is still hot.
Let cool before cutting into squares.