Lemon Rainbow Cake

Name: Lemon Rainbow Cake
Prep time: 40 min
Cook time: 20 min
Total time: 60 min
Ingredients: 550 g Butter or baking spread (softened, unsalted); 550 g Caster sugar; 4 Lemons (zest only); 10 Eggs (large); 2 tbsp Milk; 550 g Self raising flour; Red, yellow, orange, green, blue and purple food colouring (I used Rainbow Dust Pro Gel); 600 g Butter (softened, unsalted); 1.2 kg Icing sugar; 2 tsp Vanilla extract; 4-5 tbsp Milk; 275 g Lemon curd (good quality shop bought or homemade); Rainbow sprinkles

17/08/2018 by thebakingexplorer 54 Comments

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I have always wanted to make a Rainbow Cake and I decided that my birthday this year was the perfect occasion! Instead of vanilla flavour, I went for a Lemon Rainbow Cake because I absolutely love lemon cakes. The lemon zest in the sponge and the lemon curd between each layer cut perfectly through the sweetness for the perfect balance in every slice of this Lemon Rainbow Cake. Of course if vanilla is your thing, then you can easily make this cake a vanilla Rainbow Cake too!

Ingredient Tips & Equipment Information

Make sure all your ingredients (particularly the eggs and butter) are at room temperature before you start baking.
I prefer to use a baking spread like Stork for the cake, and unsalted butter for the buttercream as I find they provide the best results.
For the best results, use good quality professional food colourings. My favourite brands are Pro Gel and Sugarflair. You can buy these easily online. Other well known brands are Colour Mill and Americolor.
If you would like to make your own lemon curd for the filling, check out my Homemade Lemon Curd recipe.
Although I provide cup measurements, I highly recommend weighing your ingredients out using digital kitchen scales*. It is the most accurate way to measure ingredients and will ensure the best results. Digital scales are very low cost and can be purchased for around £12 ($16.50) .
For teaspoon (tsp) and tablespoon (tbsp) measurements, please use measuring spoons* and not the type of spoons you eat with. Again this will ensure accuracy and provide the best results.

For the full recipe with measurements, head to the recipe card at the end of this post.

How to make Lemon Rainbow Cake

To make the cake, mix the butter and sugar together with the lemon zest. Then add the eggs and self raising flour, and split the mixture between six bowls.

Mix in the food colouring, divide the mixture between the tins, then bake them. Leave to cool completely.

To make the buttercream, mix together the butter, icing sugar, milk and vanilla extract. Start stacking up the cake. Between each layer spread a thin layer of buttercream, then drizzle some lemon curd over the top.

Once the sponges are all stacked and filled with buttercream and lemon curd, cover the whole cake in a thin 'crumb coat' of buttercream. Put it in the fridge for 30 minutes to firm up. Then spread on a thicker final layer of buttercream and smooth it out. Put the remaining buttercream in a piping bag and pipe rosettes around the top of the cake. Add sprinkles in the centre and around the bottom of the cake.

What is the best food colouring to use?

To get bright shades that remains strong after the cupcakes are baked you need to use a professional grade gel food colouring. You can buy these easily from many online shops, including amazon. I used the brand Pro Gel for these cupcakes, other good brands include Sugarflair, Colour Mill and Americolor.

What lemon curd should you use?

If you are using a shop bought lemon curd, make sure to get a good quality one. They are worth the extra pennies for that delicious lemon zing! If you fancy giving Homemade Lemon Curd a try, check out my recipe. It's easy and quick to make with only a few ingredients, it's also creamy and silky smooth, and the flavour is incredible!

How can you make this into a vanilla rainbow cake?

It's easy! Simply omit the lemon curd and lemon zest, and add 3 tsp vanilla extract to the cake batter instead.

How long does the cake last for and can you freeze it?

The cake will keep in an airtight container for 3 days in a cool place. You can freeze the sponges. Once the sponges are fully cool, wrap them well with cling film or put them in an airtight container with some baking paper between them. You can also freeze the buttercream on it’s own in a tub. If you want to decorate and then freeze the cake without damaging the decoration, freeze it either in an airtight container or let it freeze solid on a cake board or plate, then wrap in cling film. Remove the cling film when you take it out to defrost it, if you don’t it could damage the buttercream as it defrosts and softens. You can also freeze slices of the cake, again well wrapped in cling film or in airtight containers.

Can you make the cake with plain/all purpose flour?

Self raising flour, which is very commonly used in the UK where I am based, already contains a raising agent and a little salt too. Therefore if you want to swap it for plain or all purpose flour, you will need to add some additional baking powder and also a little salt if you like. Some people like to add salt to cake recipes and some don't, so I'll leave that up to you as it won't affect the bake. The general advice is to add 2 teaspoons baking powder (a measuring teaspoon, not the kind you stir your coffee with) per every 200g plain or all purpose flour. So for this recipe you'd need to add 5 ½ teaspoons baking powder. Please note, I have not tested this recipe using plain or all purpose flour.

Can this recipe be made gluten or dairy free?

Yes! For gluten free you can replace the self raising flour with a gluten free self raising flour blend. If you only have a gluten free plain flour blend, you will need to add additonal baking powder. The general advice is to add 2 tsp baking powder per 200g flour, so for this recipe you'd need to add 5 ½ teaspoons baking powder. You may also like to add 1 tsp Xanthan Gum for better texture. For a dairy free version, use a dairy free baking spread and dairy free milk for the cake and buttercream. You will also need to use a dairy free lemon curd. Please check the labels of everything you use if you are serving this cake to someone with an allergy or intolerance.

Can this cake be made in different size cake tins?

Yes! If you would like to make this cake in different size tins, please check my Conversion Guide to find out how to adjust the cake recipe.

Troubleshooting

If you have any questions about this recipe, or if something went wrong and you need help, please use the comment form below and I will get back to you. You can also get in touch with me on my Twitter, Instagram or Facebook. I'd love to hear from you!

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