Purple Sweet Potato Butter Cake

My mom loves butter cakes and I've been trying out different variations of butter cakes for her. This Purple Sweet Potato Butter Cake is one of her favorite butter cake variations.

This cake is so moist, soft and fluffy and I especially love the unique aroma and purple colour from the purple sweet potato. I couldn't wait for the cake to cool down completely and cut a few slices to try while it was still slightly warm and loved it! I had some when it was completely cooled and it was also yummy but I personally preferred it when it's slightly warm.

This is definitely a keeper and I will be making more of this for sure!!

Purple Sweet Potato Butter Cake
makes a 8" square pan

Ingredients:
230g salted butter, softened
150g sugar
4 egg yolks
1 tsp vanilla extract

200g self raising flour, sifted
80ml milk

150g purple sweet potato, steamed and mashed (make sure to drain away any excess water before mashing)
1 tbspn lemon juice
4 egg whites
50g sugar

Method:

1. Remove purple sweet potato skin. Steam purple sweet potato for about 15 minutes or until sweet potato becomes soft. Pour away excess water and mash sweet potato with a fork while still hot. Weigh out 150g of the mashed purple sweet potato and set aside to cool.

2. When the mashed purple sweet potato has cooled, add some milk (about 30ml) and 1 tbspn of lemon juice to the the mashed sweet potato and mix well. (addition of lemon juice helps to keep the purplish pink colour of the purple sweet potato). Set aside.

3. Preheat oven to 160ºC. Line the base and grease the sides of a 8" square pan (greasing helps the cake’s sides to rise well)

4. Cream butter and 150g sugar until pale and fluffy. Add in vanilla extract and beat well.

5. Add in egg yolks one by one and beat well after each addition.

6. Add in the prepared mashed purple sweet potato mixture and mix well.

7. Add in half the sifted flour and mix on low speed until incorporated. Add the balance milk in 2 additions and mix until well incorporated. Mix in balance of flour.

8. Place the egg whites into another clean and grease free medium sized bowl.  

9. Beat egg whites until soft peaks. Gradually add 50g sugar and beat until stiff.

10. Fold in the beaten egg whites in 2 additions to the purple sweet potato cake batter.

11. Pour batter into the prepared cake pan and level.

12. Bake for 45 minutes or until skewer comes out clean.

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