Ma Lai Gao (马来糕)/Chinese steamed Sponge Cake

Recipe adapted from here

Ingredients
Wet Ingredients 
5 large eggs
180g coconut sugar -6oz (I use i cup) 
110g cooking oil - 4oz (I use 2/3 cup)
130g milk -4.5oz (I use 2/3 cup +1 tbsp

Dry Ingredients
280g cake flour -10oz (I use 1 cup +2/3 cup all purpose flour)
25g custard powder -1oz (I substituted with 2 tbsp cornstarch)
1 tsp baking powder - double acting
1/2 tsp baking soda
1/4tsp salt

 

Method

Mix the dry ingredients with a whisk and set aside In a large mixing bowl, beat the eggs until they are pale and fluffy with a mixer on high     speed for 5 minutes. Add in sugar, oil and milk and continue to whisk until smooth. Turn off the mixer.   Use a rubber spatula to fold in 1/3 of the flour mixture and then combine and follow by another 1/3 until you run out of flour. Do not overwork the flour.  Just stir until combined and no loose flour is visible anymore.  Line the pan with parchment paper. You can use 8-inch or 9-inch square or round cake pan. If you use 7 inch pan, make sure it's at least 3 inches in depth. Pour batter into the pan and let it rest for 30 minutes or more. Prepare your steamer by bringing the water to a boil. Pour the batter into the pan and let the cake steam for about 30 minutes if you are using bamboo steamer, and 35 minutes if you are using metal cake pan. If you choose to use smaller size, such as muffin cups, steam for about 10-15 minutes