To Decorate the Cake

• Mix together the icing sugar, butter and vanilla until it is fully incorporated. If you find the buttercream is still too thick add 1tsp of milk and mix again. Repeat until the buttercream reaches the desired consistency.
• Split the buttercream between 7 bowls. You will need more blue to decorate the outside of the cake, white for the clouds and you will also need slightly more red buttercream.
• Add the food colouring a little at a time. You need 1 bowl of red, yellow, orange, purple, turquoise, blue and leave the last one white.
• Put the red, yellow, orange, purple and turquoise into large piping bags with either a large round nozzle or if you are using disposable piping bags you can just snip the tip of the piping bag off. .
• Place your first cake onto your cake board/serving plate. Pipe the red buttercream around the edge of the cake, then pipe the yellow next to it, then orange, purple and blue, moving closer to the centre of the cake with every colour until the blue is in the centre. Stack your remaining cakes with the same technique. Once all your cakes are stacked put any left-over buttercream back into their bowls.
• Put the white buttercream into a piping bag with a large round nozzle and pipe around the outside of the cake. Smooth the buttercream using a cake smoother. Don’t worry if you can still see the cake through the buttercream this is just our crumb coat.
• Once your buttercream is smooth, pop the cake in the fridge for 20-30 minutes or until the buttercream has hardened.
• Once your buttercream has hardened, remove the cake from the fridge and pipe the blue buttercream around the sides and top of the cake. Smooth with your cake smoother. If there are any gaps fill these in using the buttercream and smooth again.
• Once your blue buttercream is completely smooth, using a rainbow cookie cutter go around the side of the cake and gently mark out where you want to pipe your rainbows. You will use these markings as a guide.
• Put your red, yellow, orange, blue and purple buttercream into piping bags with a small star nozzle. Starting with the red pipe around the top of the outline of your rainbow and work your way to the centre using your different colours.
• Once all your rainbows have been piped, pop your white buttercream into a piping bag with a large round nozzle and pipe the clouds around the edge of the rainbows. I done this by piping some splodges.
• Pipe the white buttercream onto the top of the cake to resemble the clouds and finish with some sprinkles and a rainbow cake topper.