Place the margarine, caster sugar and eggs into a mixing bowl. Sift over the self-raising flour, cocoa powder and baking powder. With an electric mixer beat everything together for 2 minutes or until smooth.
Divide the mixture equally between the two cake tins and spread out evenly.
Bake for 30 minutes.
Cool for 10 minutes before turning out on to a cooling tray.
Icing: Place all the icing ingredients into a bowl and place over a pan of barely simmering water (bain-marie / water bath). Stir until melted and smooth. Cool and spread over the top of the cake. This produces a matt icing.
Chocolate Hearts: Line a baking tray with parchment paper. Place 75g broken chocolate into a bowl, place over a pan of simmering water (bain-marie / water bath). Allow the chocolate to melt without stirring. When the chocolate has melted stir until smooth. Place heaped teaspoons of melted chocolate onto the parchment paper and spread to make circles. Place in the fridge to set. When set take a small heart cutter and cut out heart shapes. Dab a small amount of leftover melted chocolate to the underside of the hearts and place onto the cake.