Bring to boil the water,3 T.cocoa and 2 sticks of butter.Set aside.
Sift sugar,flour,cinnamon and salt into large bowl.Stir hot mixture into dry ingredients.Add eggs and soured milk into which you have added the baking soda.Add vanilla.
Pour into a greased jelly roll pan.Bake at 350 degrees for 20-25 minutes.
While cake is baking ,mix in small saucepan the 1 stick of butter,milk and cocoa.Heat until mixed.Stir in powdered sugar and vanilla. Spread om cake as soon as you remove from oven. Let cool and chocolate will set up.
We like to keep it refrigerated -it seems to stay moist longer.