This delicious coconut and lime cake filled with passionfruit curd is the obvious birthday option for budding pirates. A surprisingly simple-to-make ‘glass’ waterfall is the pièce de resistance.
Heat the oven to 180°C/160°C fan/Gas 4.
Make the cake mixture in two batches. Beat 350g of the butter and 350g of the sugar in a stand mixer fitted with the beater, on medium speed for about 5 minutes, until pale and creamy. In a separate bowl, beat together 7 eggs and gradually add them to the creamed butter and sugar, beating well between each addition. Using a metal spoon, fold in half each of the flour, baking powder, coconut and lime juice and zest, beating until just mixed. Divide the mixture proportionately between the round cake tins. Bake the 10cm and 12cm cakes for 35 minutes, the 15cm cake for 45 minutes, or until all the cakes are firm to the touch and a skewer inserted into the centres comes out clean. Leave the cakes to cool in their tins for 10 minutes, then turn out onto a wire rack to cool completely.
Use the remaining sponge ingredients to make a second batter, as before. Spoon it into the 25cm square tin and bake for 55 minutes to 1 hour, or until firm to the touch and a skewer inserted into the centre comes out clean. Leave to cool in the tin for 10 minutes, then turn out onto a wire rack to cool completely.
Make the passionfruit curd. Halve the passionfruit and push the flesh through a sieve into a heatproof glass bowl. Add the sugar, egg yolks and cornflour and mix until smooth. Set the bowl over a pan of gently simmering water and whisk for about 5 minutes, until thickened. Add the butter, a little at a time, and whisk until melted. Remove from the heat and set aside to cool (cover the surface of the curd with cling film to stop a skin forming). Once cool, refrigerate to thicken up until needed.
Make the sugar glass. Scrunch up the rectangle of baking paper and place it on the baking tray. Microwave the isomalt in a heatproof glass measuring jug in 30-second bursts until fluid. Using the heatproof gloves, take the jug out of the microwave, stir with a metal spoon and wait for the bubbling to stop, then slowly pour the liquid in a curvy strip about 5cm wide and 23cm long over the baking paper. Take care! The isomalt will scald if you touch it while it’s hot. Set aside until cold and set hard.
Make the coconut buttercream. Beat the butter in a stand mixer fitted with the beater until smooth. Gradually add the icing sugar and coconut milk and beat until thick and creamy. Set aside.
Cut all the sponges in half horizontally and sandwich each cut sponge together with a little passionfruit curd and a little buttercream. Place the square cake on the cake board and spread all over with a thin layer of buttercream. Spread each round cake with a thin layer of buttercream – leave the round cakes on the work surface.
Colour the remaining buttercream with a little blue and green food colourings to give a blue-green sea shade. Place into the large piping bag fitted with a large closed star nozzle.
Knead half the sugar paste with navy blue food colouring and the other half with dark green to give an even colour. Then, knead the two coloured pastes together to create a marbled effect.
On a work surface lightly dusted with icing sugar, roll 600g of the marbled sugar paste to a 35cm square and drape this over the top and sides of the square cake, trim the edges to neaten, reserving the trimmings.
Divide the remaining icing proportionately and roll each portion into a circle large enough to cover the top and sides of each of the round cakes. Drape over and trim to neaten, reserving the trimmings.
Stack the round cakes on top of the square cake, from largest to smallest, positioning them towards one corner of the square. Knead the trimmings with more green food colouring to make it dark green, then wrap it in cling film and set aside.
Lay the waterfall down the front of the three tiers, securing with a little buttercream from the piping bag. Pipe waves and kisses of buttercream around the base of the waterfall to look like water. Tear some of the reserved dark green fondant and squish it to look like patches of moss. Arrange this around the cake, reserving some pieces for the final decoration.
Colour half the flower or modelling paste dark brown. Push one dowel into the top of the square cake and the other into the top of the uppermost round cake. Roll the paste around the dowels to make two thick tree trunks (trim the dowels, if necessary) – use a skewer to score the paste to look like bark. Trim to neaten, reserving the trimmings.
Colour the remaining paste bright green. Roll two small balls of paste in your hands and push one on top of each tree trunk. Roll out the remaining paste thinly. Using a sharp knife, cut four five-pointed stars. Brush the ball on top of each trunk with a little alcohol and position two stars on top of each trunk to look like layers of palm leaves. Position the last, reserved pieces of dark green sugar paste ‘moss’ around the bases of the palm trees and roll any remaining brown flower or modelling paste into rough rock shapes and position these around the palm trees, too.