Purple Sweet Potatoes Chiffon Cake

Falling in love with purple sweet potatoes, love the original sweetness, colour and how it transform into a dessert. 

I think this is my 4th attempt after trying again n again to success making this purple potatoes chiffon cake. The previous 3 times fall off from the mold after cooling when it was inverted. What a dishearten when I saw the whole cake fall off from the mold.

The amount of the batter can bake one 21 cm and two small (mini) chiffon. I kept the two small chiffon in the freezer for my breakfast when I run out of bread.

I afraid the batter might turn into grey colour after mixing the yolk with the potatoes (which I encounter before) instead of purple colour so I added half of a lemon juice into the batter. Guess what? The batter turn into light pink colour, so gorgeous. I saw this idea from http://www.maameemoomoo.com/blog/2011/04/18/sweet-potato-chiffon-cake-with-white-chocolate-cream-success/  who share about this tip. Such a amazing chemistry.

There is a little sour taste perhaps it might be the lemon juice which I added. Anyway the chiffon still taste soft and cotton and the small extra added cubes potatoes within the cakes is a bonus. I wish my chiffon cake will always be a success. =D

Recipes source: Chiffon Cake Is Done, 戚风蛋糕出炉了
*Using a 21cm chiffon tin and mini chiffon tin

Ingredient A (Egg Yolk batter):
- 3 egg yolks
- 75gm cooked purple sweet potatoes (mashed) + 25gm (cut into small cubes and coat with some flour to prevent the potatoes sank to the bottom of the mold)
- 75gm coconut milk (I use low fat fresh milk)
- 1/8 tsp salt
- 30ml vegetable oil (I used canola oil)
- 1/4 tsp yam essence (I omitted)
- Few drops purple colouring (I omitted)
- Half a lemon juice
- 25gm castor sugar
- 90gm plain flour (Sift)

Ingredient B (Egg White foam):

- 3 egg white

- 50gm castor sugar

- 1/4 tsp cream of tartar

Method:

1. Separate the egg yolk and egg white into different bowl (make sure the egg white bowl do not contain any water or oil on it).
2. In a clean bowl, whisk the egg yolk with the sugar until the yolk become pale in light yellow colour. Add in the essence, colouring (if using).
3. Add in the oil (add in bit by bit) and mix well till incorporated, follow by the milk (add in bit by bit) and mix well till incorporated.
4. Add in the mashed potatoes and mix until incorporated. Pour in the lemon juice and mix (the colour will turn into light pink).  
5. Add in the sift flour and salt & mix until no trace of flour can be seen. Set aside.
6. In a separate bowl, whisk the egg whites till stiff peaks form. With a spatula, fold in 1/3 of the meringue into the yolk batter and mix. Continue mix the remaining meringue and make sure there are no trace of meringue can be seen in the batter.
7. Put the small cubes of potatoes into the batter and mix it lightly and gently.
8. Pour batters into chiffon tin, rap tins on counter several times to eliminate air bubbles.
9. Bake in the pre-heated oven at 170°C for 30-40 minutes until insert a toothpick into the centre comes out clean. Invert the tins immediately and leave to cool completely before unmold.