Preheat the oven to 180C. Grease and line 3 x 20cm round cake tins with non-stick baking paper. In a medium bowl, mix the flour, corn flour and baking powder together to combine and put aside. Place the butter and sugar in a medium sized bowl and beat until light and fluffy for about 5 minutes before adding in the vanilla essence. Beat in the egg yolks, one at a time, beating well after each addition. Next, sift in the flour mixture in 2 additions, alternating with the milk. Put the egg whites into a clean bowl and whisk until they hold soft peaks. Add the egg whites to the cake batter and gently fold together until just combined. Divide the batter equally between 3 bowls. Add a small amount of each food colouring to each bowl, enough to make 3 vibrant colours. Transfer the cake batter to the 3 prepared tins, one colour per tin, and bake for 15-20 minutes, or until they spring back when touched lightly. Allow to cool in the tins for 10 minutes before turning out onto a wire rack to cool completely.

Meanwhile, you can prepare 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. Put 190ml water and the sugar into a pan over medium heat. Bring to the boil and allow to bubble until the syrup reaches 121`c. Meanwhile, put the egg whites into a clean bowl and whisk to stiff peaks with an electric hand whisk. With the mixer still running, pour the syrup in a slow stream down the side of the bowl containing the egg 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 so if this happens don’t worry, just keep mixing and eventually it will smooth out to form a light butter cream frosting. With the mixer on medium speed, pour in the melted chocolate and mix until fully combined. 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. Spread the remaining frosting across the top and sides of the cake and decorate with coloured sweets and strawberies. Chill before serving.