Homemade Tokyo Banana 東京ばな奈

Easy and yummy recipe that you can make at home!!
I find it's quite similar to the store bought ones, except not as perfect looking of course... Same texture and taste except not as sweet. I find the original filling to be way to sweet for me... =__="

Filling Recipe:

1 medium banana
2 tbsp sugar
1 egg yolk
1/2 cup milk
1 tbsp starch
Few drops vanilla extract

Cake Recipe:

4 egg whites (one from the filling)
3 egg yolks
2 tbsp vegetable oil
40ml milk
1/4 cup sugar
1/2 cup cake flour
pinch of salt

1. Mash up the banana and add sugar.
2. Combine the egg yolk and milk, dissolve the starch.
3. Add the milk mixture to the mashed banana.
4. Strain through a sieve for a smoother texture.
5. Over low heat, stir the mixture until it thickens into a paste-like consistency and scoop the filling into a piping bag.
6. For the cake portion, combine together the egg yolks, vegetable oil, sugar and milk.
7. Sift flour into the egg yolk mixture.
8. Add a few drops of white vinegar to the egg whites and whip into peaks. 
9. To make the brown markings, take a bit of cocoa powder and combine with a spoonful of the whipped egg whites.
10. Fold the egg whites in 3 portions into the egg yolk mixture. 
11. On wax paper, dot the brown spots first, then pour the cake batter over top.
12. Smooth it out and drop the pan a few times to release all the air bubbles.
13. Bake @ 295F for around 15 mins.
14. Cover with wax paper and flip it over, remove the wax paper on the bottom side and let it cool.
15. Cut into squares, I made 9.
16. Place a square piece of cake on a clear plastic wrap and squeeze on the filling from earlier.
17. Roll it up into a cylinder shape and twist the ends closed.
18. Chill in the fridge and it's done~