Rainbow Miffy Coconut and Sweet Potato Sponge and Pudding Cake

My friend's daughter is a big fan of Miffy so she requested for a few Miffy macaron cake toppers which she can use over a few birthday celebrations for the little girl, and one rainbow sponge and pudding cake topped with one of the cake toppers I made!

You may refer to my previous post for the detailed recipe for Miffy macarons. You may fill it with fillings of your choice. I will focus on sharing the recipe for the cake in this post.

I used a reduced egg yolk chiffon cake recipe in order to get a nice blue and pink sponge without adding too much colouring. The great thing about sponge and pudding cakes is the pudding keeps the sponge moist during storage and the complentary textures of soft fluffy chiffon and smooth pudding is really nice.

Reduced yolk coconut chiffon cake
Ingredients (makes one 15cm chiffon cake):
1 egg yolk (about 17-18g)
3g castor sugar
45g coconut oil
54g coconut milk
1/4 tsp vanilla extract
A few drops pandan flavouring (optional)
A few drops coconut flavouring (optional)
1/8 tsp salt
60g cake flour
Pink, yellow and blue gel food colouring

3 egg whites
1/5 cream of tartar
40g castor sugar

Note, you can choose to bake all colours at once then slice horizontally to separate the different coloured layers or bake them individually in three rounds of baking.

I baked the colours individually as I didn't want to have the stress of ensuring all layers are perfectly level and then slicing them in perfect layers. I baked each layer for about 30-35 minutes. You may also bake the cake or cakes in regular 15cm round pans with the base lined with parchment paper.

Steps:
1. Preheat oven to 150℃ and set oven rack to lowest or second lowest position. You may choose to place a tray of water at base of oven to create steam but this is optional. Increase baking time if using steam baking.

2. Prepare egg yolk batter. Whisk egg yolk with castor sugar until pale and thick. Add oil and whisk until combined. Add coconut milk and flavourings until combined. Gradually sift in flour and salt and whisk until no trace of flour is seen. Divide the batter and add colouring as desired.

3. Prepare the meringue. In a clean metal bowl, beat egg whites with cream of tartar until firm peaks form or stiff peak is just reached, gradually adding sugar once the egg whites are foamy.

4. Quickly but gently fold the meringue into the egg yolk batter in two additions. Pour or spoon batter into chiffon tin/ baking pan.

5. Bake for 10 minutes. Reduce temperature to 130℃ and bake for another 15-20 min if you are baking single colour at a time. If you are baking a full chiffon cake, extend baking time for another 15-20 min or so. Do note that temperature and time suggested here is just a reference. Each oven behaves differently so adjust accordingly. Always use an oven thermometer at all times. Cake is done when a skewer inserted comes out clean. Invert chiffon tin (if using one) to cool completely before unmoulding by hand.

Baked chiffon layers

Store the layers in cling wrap to prevent drying out.

I baked extra chiffon sheet cakes to fill the hole in the middle and for the name on the cake. I cut out circles from the sheet cake for filling the holes.

I make use of the natural colours of different types of sweet potatoes to create the rainbow pudding layers. Here are the steamed and mashed sweet potatoes!

Steamed and mashed orange, Japanese and purple sweet potatoes.

I prepared some pandan juice that has been kept in the fridge for two days to become more concentrated, and added some to the Japanese sweet potato to colour it green.

Adding concentrated pandan juice to colour Japanese sweet potato green

As you can see the colour is rather dull. I still needed to add 1/4 tsp pandan paste to make the green more vibrant. I added 2 drops of liquid orange colouring to orange sweet potato as the natural colour is a little light when mixed with coconut milk.

A key to creating such layered sponge and pudding cakes is to carefully prepare the flexible plastic cake ring. I have tried using springform pan and adjustable metal cake rings before to assemble sponge and pudding cakes. But I find using clear flexible plastic cake rings the best option as it is versatile in the sense that it can be adapted for different cake diameter and height.

As the sponge layers are about 2-2.5cm tall, the pudding layers have to be about that height. I carefully stuck two strips of plastic together using scotch tape to form a taller wall. I also used a marker to make little dots to mark out 2cm intervals along the height so I know how much pudding to fill during assembly.

Measure out the circumference of the cake ring needed using a layer of baked sponge cake and tape the ring.

The sweet potato pudding recipe below is for one layer of pudding. You need to prepare three portions for all three colours. Recipe is adapted from here.

Recipe for sweet potato pudding
Ingredients (for one layer of pudding):
A)
200g pandan water (boil several pandan leaves in saucepan of water for 10 min.)
12g castor sugar
1/4 tsp salt
1/2 tsp agar powder

B)
73g sweet potato puree
90g coconut milk

C)
20g cornflour
34g fresh milk
1/2 tsp coconut oil (optional)

Steps:
1. Combine A) in a saucepan. Mix B) in a bowl and set aside. Mix C) in a jug and set aside.

2. Bring A) to boil while stirring, making sure all agar has dissolved before adding B) to A). Bring to boil again while stirring.

3. Stir C) again before pouring into contents in the saucepan. The mixture will thicken suddenly. Just remove from heat for a while and stir vigorously. Put back on heat and stir for another minute. Strain the mixture through a sieve to remove any lumps.

Note that you should prepare one pudding layer at a time and assemble one pudding and sponge layer at a time.

Assembly
1. Place cake ring on a sheet of aluminum foil with sides folded up. You don't need the foil if you are assembling sponge layer first and you can assemble directly on the cakeboard.

2. Place a piece of circle cutout on top of the foil in the middle.of the cake ring. This is necessary as the cake will slide off the cakeboard easily if there is no sponge to anchor the cake to the cakeboard. Spoon some purple sweet potato pudding to cover the sponge cake. When you have filled about 2cm height worth of pudding, place the blue sponge on top carefully and gently press in down. Fill the hole in the sponge with a other circle cutout cake.

3. Chill the cake in fridge while you prepare the green pudding. Repeat layering of pudding and yellow sponge. Repeat for orange pudding and pink sponge.

4. Cover the top of the cake with cling wrap to prevent the sponge from drying out. Chill for at least two hours before attempting to move the cake to the cakeboard. Carefully remove cake ring when cake is carefully positioned onto cakeboard.

I just used simple deco for the cake with marshmellows and the name in cream coloured sponge.

Not forgetting topping it off with Miffy!

My friend sent me some lovely pictures of the cut cross section. Here's a slice with Miffy too!

With love,
Phay Shing