Grease and line (with grease proof paper) an 8
                inch round microwave tray and set to one side.
                Mix the sugar, cocoa, salt, flour and
                bicarbonate of soda in a mixing bowl. Make a well
                and add the oil and vanilla essence. In this
                recipe, the raising agent is the reaction between
                the sodium bicarbonate and the vinegar (the
                acetic acid in the vinegar displacing the weaker
                carbonic acid in the sodium bicarbonate to
                produce bubbles of carbon dioxide) - the raising
                effect being lost if it is used too early or
                given a chance to escape. Add the vinegar so that
                it goes into the oil and therefore does not
                immediately come into contact with the dry
                mixture. Pour in the cold water and fold in the
                mixture. Do not beat it as this will destroy the
                bubbles. Pour into the tray and microwave for 10
                minutes at 450 Watts (around 7 or 8 minutes for
                650 watts et cetera).
                When cooked, let cool and then turn out onto a
                plate or board.
                In a clean bowl, beat the margarine and add
                the essence. Sift the icing sugar and the cocoa
                powder and mix to an even consistency. Add water,
                small amounts at a time while beating, until a
                creamy consistency is achieved.
                With a long knife, carefully slice the cake in
                two, horizontally (try introducing a piece of
                grease proof paper behind the knife as you do
                this as this will help you to separate the two
                pieces), placing the top piece down
                carefully (this recipe is not super-glued
                together with eggs so runs a higher risk of
                breaking). Spread the filling onto the lower
                piece and replace the top, making sure that the
                icing goes all of the way to the edge. If
                desired, more icing may be used to cover the cake
                completely.