Beat the sugar & butter or margarine together in a bowl until light and fluffy.
Gradually add the eggs, beating well after each addition.
Sift the fours,cocoa powder,baking powder & bicarbonate of soda together and carefully fold it into the mixture. Then add vanilla essence.
Pour into the prepared tin & bake in a preheated oven 180C for 30 - 35 minutes.
Leave the cake to cool in the tin for a few minutes, then transfer to a wire rack and leave to cool completely.
To make the syrup, gently heat water, sugar, rum together in a small saucepan
And bring to the boil for 3 minutes until soft.
Drizzle the syrup over the cake and leave for at 1 hour to allow the syrup to soak in.
Dust with the icing sugar before serving.