The butter is melted with hot water to be used later.
Mix cake flour, baking powder and baking soda and sieve them for later use.
Stir the eggs and brown sugar until dissolved.
Add melted butter and whole milk and mix well.
Add the sieved flour, stir evenly, filter, and let it rest for 30 minutes.
Pour into a paper cup until it's 90% full, and steam on high heat for 15-20 minutes or until cooked (the time depends on the size of the cup, the water must be boiled before you start steaming)