In large bowl, sift together flour and sugar. Bring to a boil the following: margarine, Crisco or cooking oil, water, and cocoa. Whip into flour and sugar. Mix together eggs, buttermilk, soda and vanilla and then add to mixture. Batter will be thin. Bake in a large sheet pan or 2 small sheet pans at 350 degrees about 25 minutes or until done. Icing: Bring to a boil: margarine, cocoa, milk, powdered sugar and vanilla. Mix while hot. Pour on warm cake. 1/2 cup chopped nuts may be added to icing.