Makes 1 cake
1 Grease and line two deep 8in tins with parchment paper.
2 Using an electric mixer, cream 300g of the butter and the caster sugar together until pale and fluffy. Add the eggs with a sprinkle of the flour to stop it curdling before adding the remaining flour and orange zest. Beat briefly until thoroughly combined and split between the two tins. Bake for 20-30 minutes at 180C/Gas Mark 4 until risen and golden. Allow to cool.
3 While the sponges cool, make the chocolate filling by combining 100g of butter, 250g of icing sugar, 75g of cocoa powder and the orange juice in an electric mixer and blitzing until you have a smooth consistency.
4 Carefully slice each cake horizontally so you end up with four thin layers of sponge. It’s best to assemble the cake on the board you are planning on serving it on to avoid a risky transfer.
5 Take one layer of sponge and spread it with one third of the chocolate filling, then top with another layer of sponge. Repeat the process, finishing with the flat edge of a layer of sponge, to give a nice even top to the finished cake. Pop this in the fridge to chill whilst you make the vanilla frosting.
6 Beat 200g of butter, 500g of icing sugar, 1 teaspoon of vanilla extract and boiling water in an electric mixer until you have a light and fluffy texture – add more boiling water if it feels too stiff to spread. I used a couple of drops each of green and blue colouring for a “robin’s egg” blue. shade.
7 Use a spatula to spread the buttercream on to your chilled cake, over the top and down the sides until it is evenly and smoothly covered.
8 To finish, mix the 2 teaspoons of cocoa with a teaspoon or two of vanilla until you have a liquid paste. Using a clean paintbrush, dip it into the cocoa mixture and flick the brush against the handle of a wooden spoon so that it sprays droplets against the cake.
9 Finish with a little pile of grated chocolate or fondant eggs in the centre of your cake.