Sift the flour, baking powder, baking soda, and salt together.
In a bowl, mix ripe bananas and sugar together. Use cake-mixer beat for 5 minutes with medium speed. Add egg one by one and beat until all ingredients mix well.
In another bowl, add fresh milk and vinegar. Add cake flour and then soybean oil. Beat all ingredients for a minute with spatula.
Prepare the steamer 10 minutes in advance and make sure the water is boiling before you put in the cake.
Lined the base of the cake pan with baking paper. Pour the cake into a lined and steam at high heat for 12 – 15 minutes.
