Prepare custard filling: Combine custard powder, milk powder, coconut milk, eggs, and condensed milk in a bowl.

Whisk until lump-free, then add melted butter.

Grease a steaming container and sieve the custard mixture into it.

Preheat steamer until water boils.

Steam custard for 12-15 minutes.

Mash the steamed custard with a spoon and let it cool.

Form the cooled custard into small balls.

Grind black sesame seeds into powder.

Combine sesame powder with all-purpose flour.

Activate yeast in lukewarm water with sugar.

Add yeast water and vegetable shortening to the flour mixture and knead into a soft dough.

Cover and let the dough rise for 45 minutes or until doubled.

Divide dough into 18-20 parts and roll into balls.

Roll each ball into a thin disk.

Place a custard ball in the center of each disk.

Close the dough around the filling to form a bun shape.

Place buns on a greased baking sheet, seam side down, and let rest for 15-20 minutes.

Grease a slotted steaming plate.

Steam buns for 10-12 minutes, leaving space between them.

Let cool slightly before serving.