how to make steamed sponge cake (bolu kukus)

Ingredients:

    5 egg yolks
    4 egg white
    250 gram granulated sugar
    300 gram flour
    ½ tsp baking soda
    175 cc soda water (Sprite/7Up)
    ½ tsp vanilla
    1 Tbs cocoa for coloring

Instructions:

    Cover approx. 20 tin cups used to steamed the cakes with parchment papers then put them into a steamer pot with boiling water.
    Mix egg yolks, egg white, baking soda, sugar and vanilla until they make a smooth batter then put in turns, ½ portion of the flour, ½ portion of the soda water until all of them are used, mix well.  Take 5 Tbs of the batter and put it in a separate bowl.  Pour in the cocoa and mix well.
    Pour the white batter into the tin almost to the top then pour in 1-2 tsp of the cocoa batter on top.  Do this until all the batter is used up, ± 20 tin cups.
    Close the steamer lid, let it steamed for  ± 20 minutes with high temperature.  Then use low temperature for another 5 minutes. The cake is ready to serve if it looks like the above picture.

For 20 tin cup cakes