Traffic Light Rainbow Cake

Preheat the oven to 160°C (fan forced), and grease and line a 20cm round baking tin.

Sift dry ingredients together, set aside. Cream butter and sugar together in a stand mixer, or in a bowl using an electric whisk.

Stir the vanilla into the milk, and then, mixing on a low speed, alternatively add the milk and dry ingredients to the butter and sugar, until everything is added. There should be no streaks in the batter, but do not overmix.

Whisk the egg whites to stiff peaks, and then fold them into the cake batter. Divide the batter between five bowls, and tint each bowl to the desired colour, using the food colour gels of your choice.

Bake the layers one at a time for approximately 10 minutes. Wash and re-line the tin between uses. Leave the cakes to cool completely on a rack.

Beat the butter till almost white, and very aerated. Add 1 cup of the sugar and beat it in. Add the lemon juice, raspberry powder (if using), vanilla bean paste, salt, and the remaining sugar and beat till light and creamy.

Set aside 1½ cups of icing for the outside. Evenly divide the same amount of icing between the 4 cale layers and sandwich together as you go. The buttercream doesn't need to be thick. Finish the cake with the buttercream, smoothing all over and refrigerate to set.

Knead the ¾ of the Ready to Roll Icing until smooth, then roll out evenly using a bit of pure icing sugar to stop it sticking to the bench. Measure the frosted cake, from one side across the top and over the other side to work out how big you need to roll out your white icing.

Once the icing is rolled out large enough, roll the icing over a rolling pin and onto the cake smoothing down with a cake smoother or a soft piece of muslin or a teatowl. Set aside.

Take the remaining fondant icing, and divide into 5 pieces. Working with one piece at a time, add a small amount of gel food colour, and knead until the icing has an even tint. When all the icing is coloured, roll the pieces out to about the thickness of a 50 cent coin, and cut out circles of different sizes.

To glue the circles onto the cake, mix about 1/4 of the egg white, with enough icing sugar to make a glue-like consistency. Use a small amount of the glue mix to adhere the icing circles to each other and the cake in whatever pattern you like.