The texture of this cake is soft, moist and spongy because of the high sweet potato content, which is really good at retaining moisture (even in breads). The coconut goes awfully well with the sweet potato and the baking aroma was amazing.
There is some science to the lovely purple hue when I was researching on the net. Apparently, people have been getting bluish grey tone. The colour in purple potato reacts with acid and turns red, it reacts with alkaline and turns bluish grey. So adding some lemon juice to the purée will help you get the purple Colour. Avoid adding baking powder or soda.
The current taste is less sweet, up the sugar by 10g to 20g if you like, especially if the sweet potato you have gotten is not sweet enough.
Recipe (adapted from Bean Panda)
- 100g purple sweet potato puree
- 1-2 tsp lemon juice
- 60g coconut milk
- 4 egg yolks
- 30g caster sugar
- 1/3 tsp salt
- 50g cooking oil
- 75g cake flour
- 2 tbsp milk (optional)
- 5 egg whites
- 50g caster sugar
- 1/4 tsp cream of tartar
1. Boil potato with skin intact till soft. Remove skin, mash and strain through a sieve to get 100g of purée.
2. Add lemon juice and mix well, see the deep red.
3. Add coconut milk and mix.
4. In a separate bowl, beat egg yolks, salt and sugar till light and fluffy. Then add the oil.
5. Add in potato purée in 3 batches and whisk till all dissolve.
6. Add the sifted flour and fold gently till no trace. If batter is very lumpy, add the 2 tbsp of optional milk. Set aside.
7. Beat egg whites till frothy, add Cream of tartar. Keep beating and add sugar in 3 batches till firm peak.
8. Add 1/3 of meringue to yolk batter to lighten it. Pour yolk batter back into meringue and fold gently with spatula till evenly mixed.
9. Pour at a height into 7″ Chiffon tin. Tap a few times on counter top. Bake at 165 deg C for about 30 min till skewer comes out clean. Actual time depends on your oven as one reader took 45 min. Invert to cool.