Oreo-Banana Sponge Cake / 奥利奥香蕉海绵蛋糕 / オレオバナナスポンジケーキ

I hated the heat during hot summer days in August, really looked forward to autumn. Simply love awesome autumn in Kyoto, the weather, the food and the momiji (Japanese maple) of course. It is here! As the weather getting cooler, I feel comfortable working in the kitchen even when the oven is on. So, here come this oreo-banana sponge cake that was on my to-bake list for long.

I used a pack of 70g oreo cookies the I hid from my boys, personally I think it would be nicer with more cookies or chunks of brownie. Otherwise, it was moist and fluffy with right sweetness. Coffeeholic me had it with iced coffee, but I bet it will get along with tea too. Enjoy!

Ingredients (18.5cm round pan):
A:
4 no. egg yolks
20g sugar
1 tsp vanilla oil

B:
4 no. egg whites
1tsp white vinegar
80g sugar

C:
120g cake flour (sieve together with baking powder, 3 times)
1 tsp baking powder

D:
2 ripen banana (about 180g),  mashed
50g melted butter / vegetable oil
70g oreo cookies, break into small pieces

Method:

1. Combine ingredients A in a bowl, whisk until light and fluffy. Set aside.
2. In another mixing bowl, whisk egg white until foamy then add in vinegar and sugar. Continue to whisk until soft peaks (creamy, when lift the beater up it will have about 5 cm "tail" or "horn"). 
3. Transfer 1/4 of the egg white into egg yolk mixture, fold to combine. Then add in the rest of the egg white, fold to just combined. 
4. Fold in flour gently, then fold in mashed banana.
5. Transfer some batter to mix with melted butter, return butter mixture into the batter. Fold to combine. 
6. Add in oreo cookies (with cream), mix gently. Transfer batter into baking pan lined with baking paper at the bottom.
7. Bake in preheated oven, 160C for 50 minutes or until it is done. To check, insert a skewer in the center of the cake if it comes of clean means it is done, and otherwise.

This is "folding" in baking, video credit to Manangkuh on youtube.