1. Preheat the oven to 170 Fan. Grease and line the base and sides of 3 x 15cm /  6 inch loose-bottomed cake tins with non-stick baking paper. Set aside.

For the sponge:

1. Using an electric whisk, whisk together the butter, sugar and orange zest until light and fluffy. Whisk in the eggs, flour and baking powder until you have a smooth batter.
2. Divide the mix equally between the prepared tins and smooth over the tops. Bake in the preheated oven for around 20 minutes or until well risen, golden and a skewer inserted into the centre comes out clean. Remove from the oven and leave to cool for 15 minutes before removing from the tins and placing on wire racks to finish cooling completely.

Meanwhile, make the buttercream:

1. Beat the softened butter until smooth, then gradually beat in the icing sugar (if you add it all at once it will spray everywhere, covering you in a sweet cloud of icing sugar). Add the marmalade and continue beating until smooth. Set aside.
2. Next, make the chocolate ganache: put the chopped chocolate into a large heatproof bowl and set aside. Pour the cream into a saucepan, add the sugar and bring to a simmer over a medium heat, stirring continuously until the sugar has dissolved. Remove from the heat, pour over the chocolate and whisk until smooth and glossy. Leave to stand until thickened slightly - but still runny enough that you can pour and spread it over the cake.

To assemble:

1. Place the first cake on a flat serving plate and spread evenly with a layer of the marmalade buttercream. Add the second cake and another layer of buttercream. Top with the final cake, then pour over the chocolate ganache and use a palette knife to spread it down the sides in a smooth and even layer. Decorate with curls of orange zest.