For Filling, beat butter and icing sugar, add the remaining ingredients and mix until well-combined. Refrigerate the custard filling until cold and firm.

With an ice-cream scoop, scoop the custard filling into 10 portions. Keep in the refrigerator with cling wrap overnight.

For pau dough, mix all pau dough ingredients, knead until dough is smooth, and then let it rise for 1 hour.

Divide dough into 10 portions, flatten with palm to make wrapper. Place a custard ball at the center and seal the wrapper. Turn the pau over so that the sealed surface is underneath.

Place each pau on paper cup liner or a small piece of baking paper and rest for 20 minutes.

Steam pau at medium heat for about 10-12 minutes.