Banana deco roll

I attempted to start a lock-down bakeoff online and for the first challenge I set swiss roll or babka. It may die a prompt death if no one joins me but at least I tried. There's something addictive about designing challenges and I have a shedload. Geeky bake idea queen - and out there I'm guessing some frustrated producer of Bakeoff is dreaming of filming a football documentary or something.

Here was my swiss roll anyway. I have previously made the Tokyo Banana recipe from here and whilst it makes the best sponge, the custard flowed straight out. It tasted really nice though and I need to work on that, but for this I wanted an actual banana custard and therefore I turned to this site for a creme patisserie recipe which I adapted to my ingredients.

Decopaste:
1 egg white
30g caster sugar
40g plain flour
20g butter
Food colouring.

Method:

1. Mix everything together in the order above.
2. Divide into bowls and colour with food colouring or in my case, some cocoa powder.
3. Place into piping bags/piping cones made with greaseproof paper.
4. Pipe a pattern onto your lined baking tray and freeze for at least 15 minutes.
   NOTE: The mix probably makes enough for two trays if your pattern is quite sparing like mine. To achieve the banana design I drew banana outlines with the brown, then squeezed yellow into the gaps before using a skewer to spread the mix into the edges of the outlines.

Cake:
4 Egg whites
40g caster sugar

4 Egg yolks
40g caster sugar
1 tsp vanilla extract

45g cake flour (or plain mixed with some cornflour)

Cake soak:
2tbsp caster sugar
1tbsp boiling water

Method:

1. Preheat oven at 170C.
2. Whisk egg whites and caster sugar to a stiff meringue.
3. Mix egg yolks, caster sugar and vanilla together and then sprinkle cake flour over and combine.
4. Fold egg whites into egg yolk mix (traditionally best if you take a good scoop and beat it into the egg yolks to lighten the mix and then add the rest in a few batches folding gently to retain the air bubbles.)
5. Spread cake mixture gently over the prefrozen deco paste.
6. Rap the tin several times to be remove any big bubbles.
7. Bake for 25 minutes.
8. Peel parchment off promptly after removing from oven. (Save to use for rolling the cake.)
9. Make a cake soak/syrup by mixing sugar in boiling water.
10. Brush hot cake soak over the cake whilst it is still warm, then allow the cake to cool completely.
    NOTE: This step is extra useful here to keep the cake soft and bendy for rolling as well as keeping it moist.

Filling:
2 cups double cream (can use milk)
6 tbsp sugar
Pinch salt
3 tbsp cornflour
1 tbsp vanilla extract
3 egg yolks
1 egg
3 tbsp unsalted butter
1 mashed banana

Method:

1. Put all the ingredients bar the butter and cream into a bowl and whisk together.
2. Boil cream and pour over the eggs, whisking all the time.
   NOTE: a teatowel under the bowl helps stop it moving.
3. Pour the mix back into the saucepan and continue heating and whisking until thickened.
4. Whisk in butter quickly, add mashed banana and leave to cool in a bowl.

Construction:

1. Trim sponge edges off.
   NOTE: you can leave them on and trim after, and generally I do that as well, however sometimes you get a crispy edge that renders your roll slightly triangular and then proceeds to crack.
2. Place sponge design side down on the parchment paper (used side down or risk getting crumbs all over.)
3. Slather custard on the plain side of the sponge, not going too close to the edges to allow for squeezing.
4. Roll from the short side to get more swirl potential.
5. Cling film the whole roll and chill in fridge to set the shape.