Banana Custard Cake

Ingroients for banana custard cake (pan size 23 x 23cm or 9 x 9in)
1 cup = 240ml, 1 tbsp = 15ml, 1 tsp = 5ml
Custard cream
1egg
40g sugar (3 tbsp)
a pinch of salt
1 tsp vanilla extract (5ml)
1 tbsp corn starch (10g)
200ml milk (1 cup)
The cake batter
240g all purpose flour (2 cups)
2 tsp baking powder (8g)
1/4 tsp salt
2 eggs
80g sugar (1/3 cup)
1 tsp vanilla extract
2 tbsp melted butter