23 April 2013

Rainbow Cake once more

Recently, I received an order for a Rainbow Cake from a friend E, who is celebrating his son's upcoming birthday.

Was considering whether to use the previous recipe attempted for dear son's birthday or try the other recipe by Whisk Kid that I was interested in. As it was also the hubby's birthday recently, I took the opportunity to test-bake Whisk Kid's recipe.

I decided to go for 7" round cake as my friend's cake is supposed to be for 10 pax. I reckoned the cake would be too tall if it were 6". But since it's only a test-bake, I just did a 4-layer cake instead of actual 7-layer one. As such, I halved Whisk Kid's recipe. For the buttercream, I also used Whisk Kid's Lemony Swiss Meringue Buttercream, and adjusted the ratio accordingly, enough to crumb coat and frost the cake.

The cake turned out beautifully, and in fact the texture was slightly more tender than the previous recipe, which was curious because Whisk Kid's recipe uses lesser sugar and butter comparatively. Or could it be the eggs? Whisk Kid uses only egg whites and lululu uses full eggs? I have no idea. But the cake's texture is still not as tender as I like. Probably I would use cake flour for the actual cake.

As for the lemony buttercream, I thought that the lemon extract was too sharp for my liking. Hubby had the same though as well. But the lemon taste did provide a slightly refreshing change to the otherwise vanilla base cake. Probably I will add lemon juice instead of extract, or explore other lemon buttercream recipe.

Rainbow Cake
(7", 4 layer, recipe from Whisk Kid)

  • 213g plain flour
  • 2 tsp baking powder
  • 1/4 tsp salt
  • 113g unsalted butter, slightly softened
  • 213g caster sugar
  • 3 egg whites (I use 2 x 60g eggs and 1x 50g egg), room temperature
  • 1 tsp vanilla extract
  • 180g fresh milk, room temperature
  • Red, green, yellow, blue gel colouring
  1. Preheat the oven to 175 degree celsius. Grease 4 x 7" cake pans and line with parchment paper. (Alternatively, grease the cake pans and dust generously with flour, then tap away excess flour). Set aside.
  2. Sift the flour, baking powder and salt into a large mixing bowl. Mix well and set aside.
  3. Cream the butter and sugar until light and fluffy.
  4. Add the egg whites gradually, then add the vanilla extract and mix until incorporated.
  5. Add the flour mixture in 3 additions, alternating with milk, until just blended. Stop to scrap down sides of the bowl with spatula as necessary.
  6. Total weight of batter is about 830g. Divide into 4 portions (each about 205g - 208g).
  7. Add food colouring to each portion using toothpick, bit by bit to desired colour tone. Mix thoroughly to ensure all the colouring is well blended with the batter.
  8. Pour batter into cake pans and smooth the surface. Bake for about 13 to 15 mins.
  9. Place the cake pans on a wire rack to cool for 15 mins. Invert the cakes onto rack and let cool completely. If not frosting immediately, wrap each layer individually with clingwrap.
Lemony Swiss Meringue Buttercream
(with some excess)
  • 8 egg whites
  • 320g caster sugar
  • 360g unsalted butter, softened
  • 1.5 tsp lemon extract
  1. Place egg whites and sugar in a mixing bowl over a pot of simmering water. Using a hand whisk, beat continuously until sugar has completely dissolved. The egg whites should feel hot to touch. Remove from heat.
  2. Transfer mixing bowl to electric stand mixer and beat at high speed using whisk attachment till meringue is thick, glossy and cool down to room temperature.
  3. Reduce speed to medium and add softened cubes of butter gradually. Continue mixing until the meringue turns into a silky smooth texture of buttercream. *It may seem like a long time, but the switch in texture can happen quite sudden, be sure to watch closely.
  4. Add the lemon extract and mix till well-incorporated.
  5. To assemble the cake, place one cake layer on a serving plate/tray and spread some buttercream evenly. Repeat this process until all cake layers are stacked.
  6. Crumb-coat the top and sides of the cake, and place the cake into the fridge to chill for 30 mins.
  7. Frost the cake and garnish as desired.
  8. Chill the cake to set the frosting. Leave in room temperature for at least 1 hour before serving.


  1. How about using lemon zest instead? Then it won't be sharp like lemon extract (probably)?

    - Lelania

  2. Hi Lelania, thanks for the suggestion. I didn't want specks of zest on the cake so didn't use zest. May try lemon juice, or just add lesser extract perhaps :)

  3. Hi, if don't have 4 7 inch pans, can the batter wait?


  4. Hi Michelle,
    Yes this batter can wait.

  5. Thank u for ur reply. Is it after mix, all batter can wait or it depends on the ingredients? I like your blog...the colours, the details.... And that you sell cakes n yet share the recipes. I have a qn on the cheese bread, I will post it there...

  6. Hi Michelle,
    For this batter, after mixing the colours and all the steps, the batter can wait. Sometimes when I bake bigger cakes, I also don't have enough baking tins and have to take turns to bake.
    Actually, I only share this particular rainbow cake recipe where the cake layer is more dense and heavy. The other one that I sell, the sponge cake one which is very tender and light, I haven't share yet, coz it's a complicated method, and literally prepare batter layer by layer and bake layer by layer. So I'm not sure whether to share that yet or not.

  7. Hi, I'm really impressed by your research into rainbow cake sponges! Thanks for sharing your learnings with us. May I know which brand of food coloring you typically use? Your pastel-colored ombré cakes look so lovely. Increasingly, people seem fearful of artificial coloring - any natural coloring that you know of and would recommend? Thank you.

    - Lin

  8. Hi Lin,
    I use Wilton gel paste, just a tiny bit (tint using toothpick) is enough to colour the cakes. I haven't been exploring natural colouring because artificial colouring allows more consistency at the moment. If I do have the time to explore natural colouring, I will update in the blog.

  9. Can I use self raising flour to substitute plain flour?

  10. Hi Sharling,
    I've not tried baking using self-raising flour. Self-raising flour is actually all purpose flour with baking powder (and some with added salt as well). I'm not sure about the exact replacement, probably you can try omitting the baking powder and salt or search the internet for substitution formula.