In a bowl, whisk together the egg yolks and sugar until the sugar has mostly dissolved.

Gradually add the milk, cake flour, cornstarch, and milk powder, stirring well after each addition to ensure the mixture is smooth and free of lumps.

Strain the mixture to remove any lumps, then pour it into a non-stick pan.

Add the butter (cut into small pieces) to the pan.

Cook over medium-low heat, stirring continuously. The mixture will begin to thicken as it heats. Keep stirring to prevent burning.

After about 2-3 minutes, the custard will form a thick, smooth paste. Once it comes together, turn off the heat.

Transfer the custard to a clean surface, and while it's still warm, knead it into a smooth ball. Divide the custard into 23g portions, rolling each into a small ball. Set aside to cool.

In a large bowl, mix the all-purpose flour, yeast, and sugar together.

Slowly pour in the milk while stirring with chopsticks until the mixture becomes crumbly.

Use your hands to knead the mixture into a dough, then transfer it to a clean surface.

Knead the dough with the heel of your palm for about 5 minutes until it becomes smooth and elastic.

Roll the dough out until it's slightly thicker than dumpling wrappers.

Use a round cutter or a glass to cut out circles from the dough.

Place a dough circle in your palm, add one custard ball in the center, and fold the dough over the filling.

Pinch the edges of the dough to seal the filling inside, making sure the seal is tight to prevent leaks. Repeat with the remaining dough and custard balls.

Place each bun on a small parchment paper to prevent sticking. Place the buns inside the steamer tray, leaving space between them to avoid sticking during proofing.

Fill the steamer with warm water (30-40°C) and place the steamer tray on top. Cover with a lid and let the buns proof in the warm environment for about 30 minutes, or until they double in size.

The buns are ready when they are noticeably bigger, and gently pressing the surface results in a slow bounce back.

Once proofed, remove the bunsfrom the steamer, bring the water in your steamer to a boil.

Place the buns in the steamer and steam for 12 minutes. Keep the heat steady and avoid opening the lid to ensure proper rising.

After 12 minutes, turn off the heat but leave the lid on for another 3 minutes. This resting period helps the buns stay soft and prevents them from shrinking.

Carefully remove the lid and transfer the buns to a plate. Allow them to cool slightly before serving.