Mix together flour, sugar and salt and set aside. Combine margarine, cocoa and water, bring to a boil. Stir in eggs, baking soda and buttermilk. Mix it all well, then pour into a greased and floured sheet cake pan. Bake at 180ºC or about 20 to 25 minutes. Ice this cake while it is hot.
Icing Melt the three ingredients together in a medium saucepan, then stir in 1 entire box of confectioners sugar. Beat well, and ice the cake while it is hot.
It takes little time to make this cake, and everyone loves it. Feel free to add nuts, either in the batter or in the frosting.