For the ganache, heat the cream in a pot over medium-low heat, stirring, until just below boiling point. Place chocolate in a heatproof bowl and pour hot cream over, stirring until smooth. Chill in the fridge for 1 hour. Whip the ganache with an electric beater until light and smooth. Chill until thickened, 6-8 hours

Preheat the oven to 160°C. Grease and line the base and sides of three 20cm spring-form cake pans.

Beat butter and sugar with electric beaters until thick and pale. Add lemon zest and orange zest then the eggs, 1 at a time, beating well after each addition.

Mix in one-third of the flour, then half the buttermilk. Repeat and then beat in the remaining flour. Gently beat in the melted chocolate until combined.

Divide mixture evenly among the cake tins and bake until firm to the touch and a skewer inserted in the centre comes out clean, 25-30 minutes.

Cool in the pan for 5-10 minutes, then transfer to wire racks, right-way up. Remove baking paper and cool completely

Spread 2 of the cakes with a quarter of the ganache, leaving three-quarters to decorate. Sandwich the cakes together to form 3 layers. Use the remaining ganache to cover the top and sides of the layered cake. Decorate with truffles and coconut shavings.