Cocoa Toyko Banana Cake (Chocolate custard filling)

This post is linked to Cook and Celebrate (Christmas 2014) organised by Yen from Eat your heart out, Diana from Domestic Goddess Wannabe and Zoe from Bake for Happy Kids.

Recipe

Ingredients
Filling:
45g cooking chocolate (melted)
1/2 egg
1/2tbsp corn starch
1tbsp caster sugar (adjust according to your taste)
70g chocolate milk

Print batter:
1 small egg (separated)
1tbsp caster sugar
1tbsp cake flour
1tbsp corn starch
2tsp veg. oil
brown food colouring

Sponge:
3 egg (separated)
50g caster sugar
54g cake flour
1/4tsp salt
1tbsp milk
1tbsp veg. oil

Steps:
Filling:
1. Mix all the ingredients except melted chocolate into a mixing bowl till smooth.
2. Strain it into saucepan and cook over low heat till it thicken.
3. Remove from heat, stir in melted chocolate and set aside to cool.
4. Spoon custard into piping bag and chill in fridge. (Can prepare a day ahead.)

Print batter:
1. Preheat oven to 170C.
2. Lined and greased a 10" by 13" tray, set aside.
3. With a hand held electric whisk, whisk egg whites till frothy.
4. Gradually add in sugar and whisk till stiff peaks form.
5. Switch speed to medium and add in egg yolk, whisk for another minute until well combined.
6. Sift flour and corn starch into meringue, fold in lightly till blended.
7. Lastly fold in oil till blended.
8. Scoop 4tbsp batter into a small bowl, mix in a drop of brown food colouring.
9. Spoon batter into piping bag and pipe big dots on prepared tray.
10.Scoop 3tbsp batter into a small bowl, mix in two drops of brown food colouring to make darker brown.
11.Spoon batter into another piping bag and pipe two small dots on both side of the big dot.
12.Bake in preheated oven for 1-2mins.
13.Remove tray from oven to cool.
Note: For balance batter either make extra trays of difference prints or mix it into sponge batter for roll.

Sponge:
1. Preheat oven to 190C.
2. Sift flour and salt together, set aside.
3. With a cake mixer, whisk egg whites till frothy.
4. Gradually add in sugar and whisk till stiff peaks form.
5. Switch speed to medium and gradually add in egg yolks, whisk for another minute until well combined.
6. Fold flour into meringue lightly in 3 portions until well blended.
7. Mix milk and oil together and fold into batter until well combined.
8. Pour batter into printed tray and smooth surface.
9. Bake in preheated oven for 10mins.
10.Remove tray from oven, immediately over turn sponge onto a grease proof paper with crust facing down.
11.Peel off grease proof paper and leave it to cool on wire rack.

Assemble cake:
1. Turn sponge over and peel off grease proof paper together with crust. (You may use a sharp knife, slowly trim off crust. I didn't bother to remove the crust.)
2. Cut sponge into 6 equal pieces.
3. Tear a piece of plastic cling wrap and place it on table top.
4. Place one piece of sponge on it, pipe custard onto sponge and roll it up.
5. Twist both ends to secure roll. Do not roll too tight as sponge will be flattened.
6. Arrange cake into a semi-circle/half round loaf pan.
7. Rest cake in fridge to stabilize it shape.
8. Remove plastic wrap and serve.