Rainbow Cake with Rainbow Ruffles (V) from Showstopping Cakes

This recipe is by Rahul Mandal, author of Showstopping Cakes.

For the rainbow cake

750g unsalted butter, plus extra for greasing

750g caster (superfine) sugar

Zest of 6 lemons

2 teaspoons vanilla bean paste

9 large free-range eggs

750g self-raising flour

6 tablespoons whole (full-fat) milk

6 tablespoons Greek yogurt

Red, orange, yellow, green, blue and purple food colouring gel

For assemble and decoration

2 ½ – 3 batches of Swiss Meringue Buttercream (a recipe for this can be found on p.34 of Showstopping Cakes)

To make the rainbow cake

Preheat the oven to 180°C/160°C fan/gas mark 4. Grease six 20cm (8in) tins with butter and line with baking paper. (If you don’t have six baking tins, you can bake in batches.)

As there is so much batter to mix here, it’s easiest tp prepare in a stand mixer. (Again, you might prefer to bake in batches if you don’t have a stand mixer; the ingredients are easy to divide into three batches.)

Cream the butter and sugar together using an electric whisk or the beater attachment of your stand mixer for 10 minutes until light and fluffy.

Add the lemon zest and vanilla, along with the first egg, and whisk for 30 seconds until incorporated. Scrape down the sides of the bowl, then add the next egg and whisk again. Keep going until all the eggs are incorporated.

Next, sift in the flour and mix on the lowest speed to combine.

Take out six medium-sized bowls and add 1 tablespoon of milk and 1 tablespoon of yogurt to each bowl. Add a different colour to each one – red, orange, yellow, green, blue and purple – then whisk to combine.

Add a sixth of the batter to each of the bowls (about 450g each) and carefully fold the colour into the cake batter, without knocking out too much air.

Pour each coloured batter into one of the prepared tins and bake for 23-25 minutes, or until a skewer inserted into the middle comes out clean.

Remove from the oven and let the cakes cool in their tins for 5-10 minutes before turning out on to a wire tack to cool completely.

To assemble and decorate

This recipe requires two and a half to three batches of Swiss meringue buttercream. Keep one batch white for sandwiching the sponges and cream coating. Divide the other batch evenly between six different bowls. Colour each bowl with a different rainbow colour. It is better to use oil-based/soluble colours for colouring buttercream, as it provides a much more vivid colour.

If using gel colouring that is water soluble, mix the colours with a tablespoon of milk and whisk in the buttercream.

Take a large piping bag and fill it with a petal nozzle. Spoon coloured buttercream into the piping bag. First spoon red, followed by orange, then yellow, green, blue and purple, so as you pipe you will get one colour and a natural transition of that colour to the next.

Use a little of the white buttercream to secure the purple sponge to a 25-30cm (10-12in) cake board or cake stand on a cake turntable. Spoon 2 tablespoons of white buttercream on top of the purple sponge and spread it out using a palette knife. Place the blue sponge on top.

Repeat the process above to sandwich and stack the coloured sponges with the white buttercream, so that the ascending order is purple, blue, green, yellow, orange and red.

Coar the sides and top of the cake with a crumb coating of white buttercream, then place in the freezer to set for one hour.

Once the crumb coat has been set, you can start piping the ruffles on the sides of the cake, in a vertical direction. Hold your piping bag at the base of the cake at a right angle and, with the wide part of the nozzle touching the surface of the cake, slowly squeeze the piping bag with constant pressure while slowly piping vertically upwards. You can slightly wiggle your piping bag as you are piping to make ruffly waves, which looks pretty.

Keep going until you have covered the sides and top of the cake with rainbow-coloured ruffles. As you pipe, just make sure the ruffles are close to each other so you can’t see the crumb-coat layer underneath. Place the cake in the fridge for a couple of hours to set completely.

Once set, allow the cake to come to room temperature before serving. This cake will keep for a couple of days in the fridge.