A birthday rainbow cake

My friend Gillian is very easy to please: she just likes complicated cakes!!!

Before I had this blog, she commissioned me a “Rubik’s cube” cake for her birthday, then came the real St. Honoré, which is notoriously elaborate. And this year she decided to challenge me by requesting a Smarties-covered rainbow cake for her little bundle of joy who turned one.

The difficulty level here is not extreme: it’s just a traditional poundcake baked in six different colours, covered in cream cheese icing and decorated with Smarties. Easy, but long to make.

Luckily enough, she took care of a time-consuming task: buying the Smarties… and sorting them by colour!!! (I won’t go into the details of how her engineer husband Florian calculated the number of required Smarties… just know it involved cellular networks!) 😛

All in all, it is an awesome-looking cake that is sure to amaze your friends. I must say it feels a bit weird to eat something colourful that doesn’t match the flavour (you would expect raspberry from the red layer, lemon for the yellow one, Smurf for the blue one, and so on…), but the vanilla flavour is always good and is perfectly complemented by the cream cheese icing. It is perfect for celebrations and for kids!

Rainbow cake

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Ingredients

Cake layers

500g	Unsalted butter
500g	Powdered sugar
2	Vanilla beans
500g	Eggs (~ 10 eggs)
250g	Pastry flour
250g	Cornstarch
15g	Baking powder
As needed	Red, Yellow and Blue food dye

Icing

750g	Cream cheese (e.g. Philadelphia)
300g	Powdered sugar

Decoration

As needed

Smarties/M&M's (at least 38x9 decoration lines, you should be safe with around 400 in total)

Directions

Cake layers

1

Cream the butter with the sugar and vanilla seeds on medium speed in the bowl of a mixer fitted with the paddle attachment for around 10 minutes

2

With a spatula, gently incorporate one egg at a time

3

Finally incorporate in three times the pastry flour, cornstarch and baking powder sifted together. The batter is less delicate than an egg-based spongecake, but try to stir gently with an upward movement anyway, to prevent the air from escaping

4

Separate the batter in as many equal parts as layers you plan to bake. "Equal parts" means you should use a scale! 🙂

5

Unleash your fantasy and dye each of the parts of the batter in the desired colour for the layer. It is better to add the food dye gradually: if it's not enough, you can add more, but if it's too much, there is nothing you can do!

6

Butter and flour each cake pan and place a round of parchment paper at the bottom; then pour the batter in the mould and bake for around 25-30 minutes or until a toothpick inserted in the center comes out clean (don't open the oven door in the first 20 minutes). Let cool down on a wire-rack.

7

With a serrated knife, trim the edges of the cakes to make all layers of the same shape (and if you can, try also to remove the top and bottom of each layer)

Icing

8

Place the sifted powdered sugar and cream cheese in a bowl

9

Gently mix the two ingredients with a spatula (using a mixer didn't work for me, it made the cream cheese too liquid)

10

If you have it, prepare a cake round and spread a dash of icing on it to prevent the cake from sliding (you can also do this on a plate)

11

Spread some icing on the first layer (either red or purple, usually), then add the following layer and repeat

12

Covering the crumbs: pour some icing on the top layer and start spreading it to a thin layer all along the sides using an offset spatula with a back-and-forth movement. Slightly rotate the spatula towards the edges of the cake in order to minimise the amount of crumbs that get incorporated in the icing. This layer must be thin: its only objective is to make sure no crumbs get in the way at the time of the final icing. At the end, refrigerate the cake for at least one hour in the fridge.

13

Starting again from the top, pour the remaining icing and spread all over the cake. Remove by hand any crumbs that might get in the way

14

You can leave the icing with a "homey", indulgent look (i.e. with visible signs of the spatula) or smooth it out (to do this: keep the straight side of the spatula vertical against the side of the cake, then rotate the plate of the cake until all the excess icing has been removed

15

Gather all the patience you have and start sticking all the smarties one by one. For an 18-cm cake, I had space for 37 Smarties per line.

16

You can cover the top with more Smarties or simply add the decoration of your choice

Note

• Store the cake in the fridge for up to 5 days
• Smarties or M&M's will start losing their colour in contact with the icing, and the humidity of the fridge will not help at all, so I would suggest you finish the decoration just a couple of hours before serving, if possible
• For a normal home oven like mine, the cakes should baked on the same level to prevent over/underbaking: this means that you might have to bake in batches of two cakes. If you prefer, you can also repeat the recipe three times to obtain six layers: this was my approach but I'm not sure it is the most efficient 🙂
• Food dye might make your batter a bit "flashy", but don't  worry, since the colours will slightly darken during baking
• As a reference, orange = red + yellow; green = yellow + blue; purple = red + blue

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