Magic Rainbow Cake
Preheat the oven to 180°C (160°C fan assisted oven, 350°F, gas mark 4). Grease and line 2 x 18cm (7inch) round Victoria sponge tins. In a mixing bowl, beat one third or 75g (3oz) white vegetable fat with one third or 115g (4oz) sugar, one third or 40ml (8 tsp) milk and one third or 5ml (1 tsp) Vanilla Extract until creamy in texture.
Gradually whisk in 2 eggs and a pinch of salt. Sift one third or 125g (4 ½ oz) flour on top. Using a large metal spoon, fold in the dry ingredients smooth cake batter
Divide the mixture equally between 2 bowls. Choose 2 different Food Colour Gels and mix in sufficient colour into each batch of mixture to form a vibrant shade. We used 5g (1/6oz) each colour.
Spoon the mixture into the cake tins, smooth the tops and bake in the oven for 22-25 minutes until lightly golden and just firm to the touch. Cool for 5 minutes then turn on to wire racks to cool.
Repeat the cake making as above twice more, using the remaining ingredients and colour with the remaining 4 colours. Bake and cool as above.
To decorate, put the butter in a bowl and beat until smooth, pale and glossy. Gradually sift and beat in the icing sugar until creamy and soft. Stir in the Vanilla Extract. Add sufficient milk to make a smooth, spreadable icing.
Spread all the cakes, except the yellow layer, with 75g (3oz) icing, and stack all the layers on top of each other as illustrated, finishing with the yellow sponge on top.
Reserving 650g (1lb 7oz) of the butter icing, spread and smooth the remaining icing round the sides of the cake to cover it thinly but evenly, making sure the top edge is smooth and neat. Running the warmed blade of a palette knife, flat against the side, around the cake, will help you achieve a smooth, neat effect. Chill the cake for 30 minutes to firm up the icing. This will give you a good base to add the rest of the icing to.
Once the cake is firm, repeat the technique for covering the sides and top of the cake, this time using 350g (12oz) of the remaining icing, and spreading it slightly thicker. Use a palette knife as before to smooth and neaten the sides and top of the cake.
Divide the reserved icing equally between 6 bowls. Add a few drops of each Food Colour Gel to make bright rainbow shades. We used: 8 drops Green; 7 drops Blue; 5 drops Violet; 5 drops Pink; 8 drops Orange and 5 drops Yellow.
Starting with the Green icing, place in a piping bag fitted with a small closed star nozzle. Start at the bottom of the cake and pipe individual stars, moving upwards, in a steep diagonal wave. Take the piping over the top of the cake, stopping when you reach the other side. You may find it easier to mark out the design on your cake before you start to pipe – you can trace the direction of the pattern by gently dragging a skewer up and over the cake in the direction you want to pipe. This way you can simply pipe over the drag marks, or smooth them out if you make a mistake.
Repeat the piping with the Blue icing, piping as closely to the Green as you can. Then move on to the Violet, then Pink, then Orange and finally, pipe the Yellow. You should end up with a swirling rainbow design on one side and over the top of your cake. Your bright and colourful cake is now ready to serve, slice and enjoy!