This delicious carrot cake will taste better 24 hours after baking – which is perfect, because you’ll need to make the rainbow at least the day before you plan to serve, too – fondant icing takes about 24 hours to harden at room temperature.
First, make the fondant rainbow. Divide the fondant into 6 pieces – each piece should be slightly larger than the next.
Using the food-colouring pastes, colour the smallest piece blue, the next orange, then green, then pink, then yellow and finally the largest piece should be red.
Using your hands, roll the blue fondant into a rope 1–2cm thick and shape it into an arch. Place the arch on the lined baking sheet. Next, roll the orange fondant into a rope of the same thickness and position this over the blue arch. Keep going for each coloured fondant, ending with the red. Trim the ends of the rainbow to neaten and leave uncovered for at least 24 hours to dry.
Heat the oven to 180°C/160°C fan/350°F/Gas 4.
Make the carrot cake. Combine the raisins or sultanas with the orange juice and zest in a small bowl and warm either in the microwave or in a small pan over a low heat to rehydrate and infuse the fruit. Leave to cool while you prepare the remaining ingredients.
In a large bowl, beat together the eggs and sunflower oil until just combined. Add the sugar and mix again. Add the pecans, grated carrots, crushed pineapple and orange-soaked raisins and mix to combine.
Sift the flour, spices, baking powder, bicarbonate of soda and salt to the bowl and mix again thoroughly. Divide the mixture equally between the tins and bake for about 30 minutes, until golden brown, well-risen and a skewer inserted into centres comes out clean. Turn out onto a wire rack to cool.
While the cakes are cooling, make the cream-cheese icing. Beat the butter in a stand mixer using the beater for 2–3 minutes, until pale and fluffy. Gradually add the cream cheese and mix to combine. Add the honey, sifted icing sugar and the vanilla and mix again until smooth.
Place one sponge layer on a serving plate and spread the top with cream-cheese frosting. Place the second sponge layer on top and cover the top and sides with the remaining frosting. Chill the cake while you make the buttercream roses.
Beat the butter in the clean bowl of the stand mixer on medium speed, until pale and fluffy. Gradually add the sifted icing sugar and mix until smooth. Divide the buttercream between three bowls. Tint one portion pale pink, one darker pink and leave the remaining third white.
Spoon the white buttercream into the piping bag fitted with the petal nozzle. Using a dot of buttercream, secure a 4cm square of baking paper onto a piping pin. Pipe a cone into the middle of the square and then pipe petals around the cone building up the layers to resemble a rose. Slide the paper off the pin and repeat making more roses until all three buttercreams are used up. Chill the roses for about 30 minutes to firm up.
To serve, position the rainbow on top of the cake and the buttercream roses around.