Steamed dual layer banana lemon sponge cake (second attempt)

Recipe:

Banana cake layer

2 big banana (pisang berangan)

1 tsp baking soda

3 eggs

1/2 Tbsp molasses sugar

100g superfine flour

1 tsp baking powder

1 Tbsp coconut oil

Sponge cake layer

2 eggs

1 Tbsp molasses sugar

3 Tbsp natural yogurt

65 g cake flour
1 tsp baking powder

1/2 lemon juice
1/2 lemon zest (finely grated)

P/S: Using a 7" baking pan

Banana cake 

(1) Mix banana and baking soda, set aside.

(2) Beat eggs till foamy, add in sugar and continue to beat till ribbon stage.

(3) In sequence, mix in: sieved flour, baking powder, banana mixture in no.1 and oil. Fold till all mix.

(4) Steam in preheated steamer for 15 minutes. Once done, remove from steamer and set aside.

Sponge cake 

(1) Beat eggs till foamy, add in sugar and continue to beat till ribbon stage.

(2) Add in yogurt and lemon juice and zest. Sieved in flour and fold till all mix.

(3) Pour the batter on top of banana cake and further steam for another 15 minutes.

Results: 

The banana cake layer is very soft and fluffy.

The lemon sponge cake layer is softer than previous recipe i made: http://beejeegrace.blogspot.com/2014/09/steamed-dual-layer-banana-sponge-cake.html

However, for this time, right after steaming, the sponge cake layer was slightly sunk after it has rose nicely during steaming. I am still figuring out how to stabilise it after steaming, whole cake is harder to control compare to steam in cup cake size. Nevertheless, the result was satisfying.