Banana Roll Cake (香蕉卷蛋)

Ingredients
Banana Custard
2 egg yolks
200ml of Fresh Milk
70g of Caster sugar
15g of Cake flour/Top flour
1.5 - 2 ripened bananas (the riper, the better! adjust quantity according to your taste)

Sponge Cake
4 Egg whites
40g of Caster sugar
4 Egg yolks
40g of Caster sugar
1 - 2 drops of Vanilla essence
45g of Cake flour
1 - 2 sliced Bananas
2 tbsp of Hot water
1 tbsp of Caster sugar

Equipment: 27 x 27 cm Baking tray

Steps
Banana Custard
1. In a large bowl, mash the bananas with a whisk or fork.
2. Add half the portion of milk and the 2 egg yolks. Mix well.
3. Stir in the caster sugar, followed by flour.
4. In a pot, bring the remaining portion of milk to a simmer.
5. Pour the heated milk to the mixture in a steady stream while mixing continuously.
6. Strain the mixture through a sieve. Mash the banana lumps through the sieve.
7. Transfer it to a pot on low heat. Mix continuously until the custard thickens. The right consistency is when you can draw an "infinite" sign with the custard. Remove from heat and cover with a cling wrap (make sure cling wrap is touching the surface of custard) or transfer to a piping bag. Chill it in the fridge. 

Sponge Cake
1. To make the meringue, beat egg whites and sugar in a mixer on low speed. When it starts to get frothy, increase to medium. Beat till stiff peaks form. 
2. In a separate bowl, beat the egg yolks, caster sugar, and vanilla essence until mixture becomes creamy. 
3. Sift in the cake flour and mix till combined. 
4. Add 1/3 of the meringue in Step 1 to the batter in Step 3. Use a balloon whisk to mix, and knock against the side of the bowl to let the mixture fall. Repeat till combined, all the while being careful not to break the air in the meringue. 
5. Add another 1/3 of the meringue and fold in with a spatula. Use the same fold-and-knock motion. When combined, add the final 1/3 of meringue and fold-and-knock till combined. The batter should be smooth and shiny. 
6. Transfer the batter to a baking sheet lined with parchment paper. Gently spread the batter evenly with a spatula. Be careful not to break the air when spreading!
7. Bake in a preheated oven at 170°C for 25 minutes. Let it cool before removing from the parchment paper. Trim off the sides (don't throw them away!)
8. Mix hot water with sugar to make the sugar syrup. Spread the sugar syrup on the cake to keep it moist.
9. Spread a layer of banana custard on the sponge cake. Line the cake with sliced bananas.
10. Make 3 small incisions on each side of the sponge cake and roll gently. Wrap the cake in parchment paper and chill it in the fridge for 1 - 2 hours. You can then slice, serve, and eat! 

Reference
1. http://www.sumopocky.com/2016/01/tokyo-banana-roll-cake-recipe.html
2. https://www.youtube.com/watch?v=gjexhOPY8pw