Preheat the oven to 350 degrees. Grease a 9 by 13-inch cake pan. Combine the butter, water, and oil in a saucepan. Bring it to a boil. Add the flour, sugar, soda, salt, and vanilla. Blend in the eggs and buttermilk. Beat until smooth. Bake for 37 minutes or until done. You can also use a greased cookie sheet, bake at 350 degrees for 20 minutes. 

Combine the cocoa, butter, buttermilk in a saucepan, cook slightly. Beat in the powdered sugar and mix until smooth. Add the vanilla and blend well. Frost the cake when slightly cooled.