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If you’re after rainbow cake wow-factor without the headache of stacking seven layers, you’re in the right place. Our easy sheet cake version delivers all the colour, fun, and flavour – minus the stress! It’s great for birthdays or any colourful celebration, and the soft vanilla sponge is a winner every time. A vibrant Smarties® rainbow decoration is the jewel in the cake crown, and the little ones can help as you create the design.

Looking for colourful cookies? Try our vibrant and hearty Smarties® Oat Cookies or dip into our Easy Cookies Recipes for even more Nestlé-infused treats. If you’re in the mood for a quick and easy bake for parties, bake sales or a teatime treat, try our Smarties® Mini Vanilla Cupcakes. 

For more recipes, inspiration and tips, sign up to our newsletter. Happy baking!     

Creative decoration ideas for Smarties® Rainbow Cake 

We’ve gone with a classic Smarties® rainbow design, but you can add extra decorations to customise your rainbow cake! For even more colour and texture, sprinkle a tablespoon of funfetti or rainbow sprinkles to lightly coat the buttercream before you build your Smarties® rainbow. To add a fancy flourish, dust your finished cake with edible glitter for a magical gold-at-the-end-of-the-rainbow sparkle!  

Storage instructions 

Pop your finished rainbow birthday cake into an airtight container and store it at room temperature for up to three days. You can also freeze the un-iced cake in an airtight container for up to three months. To defrost, leave the container in the fridge overnight, then ice and decorate your cake the next day.  

How to throw a rainbow-themed party 

Keep the rainbow party magic going with colourful decorations like streamers, balloons and tableware in every colour. You can also create vibrant party bags containing 29g packs of Smarties®, crayons, colouring books and rainbow stickers to match the theme. When it comes to party food, keep things bright, fresh and tasty – you could even organise the table into colours, like the cake! Here are some ideas to get you started:  

  • Multicoloured fruit kebabs made with strawberries, blueberries and kiwi chunks  
  • Cucumber can be diced and stuck onto cocktail sticks with cubes of cheese  
  • Sliced cucumber and carrot sticks arranged around a pot of purple beetroot or orange carrot hummus
  • Cherry tomatoes, trimmed sugar snap peas and slices of red, yellow and green peppers really pop and bring the freshness
  • Corn on the cob is great fun for kids – particularly for outdoor parties where mess is less of an issue! 
     
  • 60 min
  • 24 servings

You will need

  • A square baking tin (23 x 23cm)
  • Baking paper
  • An electric whisk (optional)
  • A palette knife (optional)

For the Cake

  • 85g buttery baking spread, melted
  • 2 large eggs, at room temperature
  • 50ml water
  • 1 tsp vanilla extract
  • 180g self-raising flour
  • ½ tsp bicarbonate of soda
  • 150g caster sugar
  • 5 small bowls
  • Food gel colouring: red, orange, yellow, green and blue or purple

For the Vanilla Buttercream

  • 100g buttery baking spread
  • 160g icing sugar
  • 1 tsp vanilla extract
  • 1 Tbsp milk

For the Decoration

  • 152g Smarties® (4 x 38g tubes)
7613039905715-smarties-milk-chocolate-tube-multipack-4-pack-136g-mobile

Smarties Milk Chocolate Tube Multipack 4 Pack 136g

Each slice (1/24) typically contains:
  • Energy 688kJ 164Kcal 8%
  • Fat 7.1g 10%
  • Saturates 2.6g 13%
  • Sugars 16.8g 19%
  • Salt 0.27g 5%

of an adult’s Reference Intake (RI)*
Energy per 100g: 1836kJ/438kcal

Method

For the Cake

  1. Preheat the oven to 160°C/140° fan/gas 3 and line a rectangular baking tin (18 x 23cm) with baking paper.
  2. In a large bowl, mix in the melted baking spread, eggs, water and vanilla extract.  
  3. In a separate bowl, combine the flour, bicarbonate of soda and caster sugar, then whisk to combine.  
  4. Add the dry mixture to the wet mixture and fold until combined and glossy.
  5. Divide the mixture between the small bowls. Add 1-2 drops of each food gel colouring to each bowl and mix to combine.  
  6. Scoop the first colour into the pan and give the pan a gentle shake to move it around. Repeat this pattern with the remaining colours, stacking the layers on top of each other. Try not to mix each layer too much. Rather, tap the pan gently on the counter to spread the layers.
  7. Bake for 20-25 minutes until risen, springy to the touch and until a cocktail stick inserted comes out clean. Leave to settle in the tin for ten minutes, then pop out onto a wire rack to cool. 
     

For the Buttercream  

  1. Whisk the butter in a large bowl until light and fluffy.
  2. Gradually add sifted icing sugar, then add one tablespoon of milk and beat it until it's super smooth and creamy.
  3. Top the cooled cake with the vanilla buttercream and spread it out with a palette knife or spatula.  
     

For the Decoration

  1. Sort the Smarties® into colours
  2. Build your rainbow shape. 
     

Top Tips

To create an individually coloured Smarties® rainbow, you’ll need 11 Smarties of each colour. Alternatively, mix up all the colours and create a vibrant and multi-colour Smarties® rainbow flag pattern!  

Questions?
How do I stop Smarties discolouring on a cake?

The sugar shell coating on Smarties® provides some resistance to moisture, but it is also best to place your Smarties® on the cake shortly before you are about to serve it.  

What is the flavour of rainbow cake?

Even though our cake is the colour of the rainbow, it is flavoured with vanilla!  
 

How to stick Smarties on a cake?

A gentle press into the buttercream is all it takes to secure the Smarties® to the cake. 

What food colouring is best for rainbow cake?

Food gel colouring works well because it comes in a squeezy tube, is less messy and only requires a small amount. 
 

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