Bring butter, cocoa & water to boil. Add flour, sugar, soda, salt, eggs & buttermilk. Beat well with mixer
Pour into greased and floured sheet pan. Bake 30-40 minutes. DO NOT RINSE SAUCEPAN
In same pan, combine margarine, cocoa and milk. Bring to a boil. Remove from heat. Add powdered sugar, vanilla and pecans. Beat well and set aside.
Frost cake as soon as it is removed from the oven
Wait until cake cools and icing sets before slicing.
NOTE: You can slice and leave in sheet pan and freeze until solids. Then remove individual pieces, wrap in foil and store in freezer in ziplock bag. Thaw by unwrapping piece and bring to room temp on counter, about 30 minutes