Pre-heat the oven to 170°C.
Grease and line 2 x 8 inch springform cake tins with nonstick baking paper. Combine the cocoa powder, self-raising flour, sugar, butter and eggs in a large mixing bowl. Whisk until smooth using an electric hand-held whisk; usually 2-3 minutes. Whisk in the milk if the batter looks a little dry. Spoon into the prepared cake tin and bake for 25-35 minutes until a cake tester comes out clean when inserted into the centre of the cake. Remove and allow to cool in the tin for 10 minutes.
Meanwhile, prepare the icing by placing the chocolate in a large heatproof bowl. Place over a saucepan of gently simmer water, stirring occasionally until melted. Remove from the heat and beat in the icing sugar, softened butter and cocoa powder until you have a smooth, thick icing. Transfer a small amount of the icing to a piping bag fitted with a star-shaped nozzle. Cover the rest of the icing and set to one side.
Turn the cakes out of their tins and leave to cool on wire racks. Once cool, discard the baking paper from the bases. Sit one of the pieces of cake on a cake stand and spread with a little of the icing. Place the other half of the sponge cake on top and press down gently to secure. Spread the rest of the icing on the top and sides of the cake using a slightly damp, hot palette knife to ensure an even finish.
Decorate the sides of the cake with the chocolate curls. Pipe the icing in the piping bag around the perimeter of the cake. Decorate the cake with the chocolates stars on one side in a row. Finish by writing 'Happy Father's Day' on the cake using the Cakecraft Designer's white icing pen.
*This cake is very rich and indulgent, so it shouldn't be eaten to often. But it's perfect for those special occasions!