Say it with Rainbow Cake!

I made this delightful cake for a friend’s 30th Birthday …. it reflects her personality – she’s vibrantly insane (in a good way!!), she loves rainbows (and as a child also revelled in the hilarious antics of George, Zippy & Bungle; of the Rainbow TV programme), and it’s got lemon flavoured icing because it’s her favourite!

But most importantly, the thing that makes this cake absolutely suited to her, is the white butter icing. Why you ask? Because like my friend the smooth white exterior is classy and timeless, but once you slice into it’s core you realise that its eye-popping & crazy!! If you knew my friend, it would all make sense!

For those of you who would like to give it whirl, here’s the recipe  …..


226 g butter, room temp
426 g sugar
5 egg whites, room temp
2 teaspoons vanilla essence
426 g flour
4 tsp baking powder
½ tsp salt
355 ml milk, warmed for 30 sec in microwave to bring to room temp
Red, orange, yellow, green, blue and purple GEL food colouring.  Liquid will not be vibrant enough!


Pre-heat the oven to  350F degrees. Oil and line as many 9” cake tins you have (I have four and I just reused them). Sieve together the flour, baking powder and salt and then set aside. Cream the sugar and butter, then add the egg whites (adding them a little at a time).  Add the vanilla essence and mix well.  Then, alternating between wet and dry, add the milk and flour mixture in two parts. Divide the batter amongst six bowls and then whisk a reasonable amount of the appropriate food color into each bowl.  Note: the colour of the unbaked batter will be the colour of the baked batter!  Pour into the cake tins and bake for fifteen minutes each. When you remove them from the oven, let them rest on the cooling rack, in the tin, for ten minutes.  Then remove, cover, and place them in the fridge to cool quickly.

For the Lemon Swiss Butter Icing:

To fill and crumb coat:
9 egg whites
1 ¾ c (350 g) sugar
4 sticks (452 g) butter, room temp
2 tsp lemon extract
To frost:
5 egg whites
1 c (200 g) sugar
2 sticks (226 g) butter, room temp
1 tsp lemon extract

Cook the egg whites and sugar in a small saucepan over medium heat, whisking constantly, until the sugar is completely dissolved (test by rubbing the mixture between clean fingers; if it’s completely smooth, it’s done!). Pour into another bowl and whisk on high-speed until room temp. Then, on a medium-slow speed, add the butter, waiting until each piece is completely integrated before adding the next. After all the butter has been added, turn the mixer back to high-speed and whisk until it has come together (about five minutes).  Add the extract, whisk briefly and then use.


Stack the layers in your preferred colour order and fill and ice as you would any other cake ….. then enjoy!!


7 thoughts on “Say it with Rainbow Cake!

  1. In the words of 3 year old daughter, this cake is, “SO COOL!” You did a great job! I am thinking that I might make this as a 1/2 sheet cake for her 4th birthday party. Crazy, for sure.

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