Preheat the oven to 160C/325F/Gas 3.
For the chocolate sponge, grease two 23cm/9in cake tins with butter and dust all over with cocoa powder.
Sift the flour, bicarbonate of soda, baking powder and cocoa into a mixing bowl, and stir in the sugar.
Place the butter and milk into a small saucepan over a very gentle heat until the butter has just melted. Allow to cool slightly.
Add the syrup, eggs, and milk mixture to the bowl of dry ingredients and beat the mixture to a smooth batter with a wooden spoon.
Divide the mixture into the prepared tins and bake in oven for 40-50 minutes, until a skewer inserted into the centre of the cake comes out clean. Remove from the oven and cool in the tin for ten minutes, then turn out to a wire rack to cool completely.
Increase the oven temperature to 170C/340F/Gas 3½. Grease and line a 23cm/9in cake tin.
For the orange sponge, sift the flour, baking powder and bicarbonate of soda together in a bowl and set aside.
In another bowl, cream the butter and sugar together with an electric hand-held mixer for 4-5 minutes until very pale.
Beat in the eggs, one at a time, beating very well between each one. If necessary add a spoonful of the measured flour with each egg to prevent the mixture from curdling.
Beat in the orange zest. Add the flour mixture all at once and fold in thoroughly, then slowly fold in the orange juice.
Spoon the mixture into the prepared tin and bake for 45-50 minutes or until a skewer inserted into the centre of the cake comes out clean. If it starts to brown too quickly, cover loosely with a piece of buttered foil.
Remove from the oven and leave the cake to cool for ten minutes in the tin, and then turn out to cool completely on a wire rack.
For the chocolate ganache, heat the cream in a pan, stirring occasionally, until just under the boil.
Place the chopped chocolate into a bowl and pour the hot cream over. Stir until the chocolate has melted and the mixture is smooth. Allow to cool for about an hour or until thick enough to spread.
For the orange cream, whisk the cream until soft peaks form when the whisk is removed. Fold the orange zest into the cream.
Place one chocolate layer onto the serving plate. Spread half of the orange cream filling on top.
Place the orange cake on as the next layer and top with the remaining orange cream. Place the last chocolate layer on the top.
Spoon the ganache over the cake, smoothing with a palette knife until the cake is completely covered.
Roll out the chocolate fondant icing to a thickness of 2mm. Using the cake tin as a guide, cut out a 23cm/9in circle. Place carefully on top of the cake. Place the stencil on top of the fondant and sprinkle over the gold lustre dust. Remove the stencil to reveal your pattern.