In a mixing bowl, combine the egg yolks, white sugar, milk, milk powder, flour, cornstarch, and butter.

Whisk the mixture until smooth and free of lumps.

Then, strain it with a strainer or sieve into a non-stick saucepan.

Heat the mixture on low heat and keep stirring continuously.

Continue heating the mixture until it becomes thick enough to form a ball. The custard should clump together and become paste-like. This should take about 10 minutes to form.

Divide the custard filling into 12 equal parts and shape them into round balls.

In a separate bowl, combine the all-purpose flour, yeast, and water.

Knead the mixture into a dough until it becomes smooth and elastic.

Roll the dough into a long strip and divide it into 12 equal pieces, about 1 inch wide.

Take one piece of the dough and flatten it into a circular dough wrapper using a rolling pin. Make the center thicker than the edges. It is better to make the center thicker than the edges to make it sturdy enough to hold the filling,

Place one portion of the custard filling in the center of the dough wrapper and seal it by pinching the edges together and rolling it into a smooth ball.

Repeat the process with the remaining dough and custard filling.

Place the buns in a steamer lined with parchment paper and cover with a lid.

Let them rest and rise for about 40 minutes.

Then, let them cook in cold water. Once the water in the steamer is boiling, steam the buns for approximately 12 minutes.

Turn off the heat and let the buns sit in the steamer for an additional 3 minutes.

Enjoy these delectable Egg Custard Buns while they're warm! For leftovers, keep it in a zip-lock bag and freeze it. Simply reheat it by steaming it whenever you crave it.