White Chocolate Rainbow Cake

This cake is a monster – it has six layers and uses a lot of butter, but do keep in mind that it will serve a lot of people, and it will make a spectacular cake for a birthday or any other occasion. The beauty of this cake is that, apart from being rather large, it looks quite innocent from the outside, because the white frosting hides the multicoloured rainbow inside. Imagine people’s reactions when it is first cut into – it’s well worth the effort.

White Chocolate Rainbow Cake

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    700 grams caster sugar 325 grams plain flour
    2 teaspoon vanilla extract 4 1/2 teaspoon baking powder
    4 medium eggs, lightly beaten 1/2 teaspoon salt
    300 millitre whole milk 150 grams white chocolate
    gel food colouring in red, yellow, orange, purple, blue and green 6 medium egg whites
    765 grams unsalted butter, at room temperature, plus extra for greasing


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    • 1

      Preheat the oven to 180°C (160°C fan oven) mark 4, then grease and line three 20cm round cake tins with baking parchment, greasing the parchment too. In a medium bowl, whisk the flour, cornflour, baking powder and salt together to combine, then set aside.  

    • 2

      Put the butter into a large bowl and, using an electric mixer, beat on medium–high speed until smooth and light. Add the sugar and beat until light and fluffy, about 5 minutes, then add the vanilla and mix to combine. With the mixer on medium speed, add the egg yolks, one at a time, beating each until fully combined before adding the next. With the mixer on low, sift in the flour mixture in three additions, alternating with the milk, starting and finishing with the flour.

    • 3

      Put the egg whites into a clean, grease-free bowl and whisk until they hold soft peaks. Add the whites to the cake batter and gently fold together until just combined and there are no streaks of white. Divide the batter equally between six small bowls. Add a small amount of each colouring to each bowl, enough to make it a vibrant colour. Add the first three bowls to the prepared tins and bake for 15 minutes or until they spring back when lightly touched. Allow to cool in the tins for 10 minutes before turning out onto a wire rack to cool completely. Repeat with the remaining three portions of batter.  

    • 4

      To make the frosting, melt the chocolate in a heatproof bowl set over a pan of gently simmering water, making sure the base of the bowl doesn’t touch the water. Remove from the heat and allow to cool.  

    • 5

      Put 190ml water and the sugar into a pan over medium heat. Bring to the boil and have a sugar thermometer ready. Meanwhile, put the egg whites into a clean, grease-free bowl (this is best done using a freestanding electric mixer). Start whisking the whites on high speed when the syrup in the pan reaches about 115°C on the sugar thermometer. Cook until the syrup registers 121°C. With the mixer still running, pour the syrup in a slow stream down the side of the bowl containing the whites, avoiding the beaters. Continue whisking on high speed until the meringue is at room temperature.With the mixer on medium–high speed, add the butter a few pieces at a time, beating until fully combined. When adding the butter it can sometimes look curdled; if this happens don’t worry, just keep mixing and eventually it will smooth out to form a light buttercream frosting. With the mixer on medium speed, pour in the melted chocolate and mix until fully combined.

    • 6

      To assemble the cake, put the purple cake layer on a cardboard cake board or serving plate and top with a thin layer of frosting. Repeat the process with the other cake layers in the order of a rainbow (purple, blue, green, yellow, orange, red) and then spread the remaining frosting across the top and sides of the cake.

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