Custard Filling

1. In a small pot, whisk eggs and milk together. Then add sugar and salt, and mix well.
2. Sift cake flour and milk powder into the mixture, mix well until there are no lumps. Then add butter and place the pot over low heat. Keep stirring the mixture until thicken. Once the egg mixture solidifies into a thick custard, remove from the heat.
   
3. Transfer the custard onto a plate/bowl. Let cool, cover with plastic wrap and refrigerate it for later use.
   

Bun Dough

1. Stand Mixer: In a large mixing bowl, combine milk, yeast, sugar, flour, and oil. Using dough hook attachment, mix on low speed for 5 minutes, then increase to mediums speed and mix for another 5 minutes. Mix until the dough is white and smooth.
   Kneading by Hand: Mix yeast and sugar with milk. Stir in flour and mix. Then add oil and start kneading. Use one hand to push the dough then pull it back. Alternating hands, repeat this motion for 8-10 minutes, until the dough is smooth and shiny in appearance. (You should be sweating by then!)
2. Take the dough and divide into 10 equal portions (50 g each). Cover with plastic wrap or towel to prevent them from drying.
3. Roll each piece of dough into a log. Then take both ends and fold toward the middle. Press down with the palm of your hand. Repeat this two more times to get rid of air bubbles.
   
4. To ensure that the bun has a smooth surface, use your palm to fold the edge toward the middle (2). Gently press down in the middle. Then slightly rotate and do it a few more times, until all edges are nice and round with no cracks or lines. If you turn the dough upside down, the top will look very smooth (4), and the bottom will look like belly button (3).
   With the belly button side facing you, flatten the dough ball again using your palm (5). Use a rolling pin to roll the ball into a round disc that is thick in the middle and thin on the edges (6).
   

Assembly

1. Divide custard filling into 10-12 equal portions. Place custard filling onto the center of the wrapper disc, pleat, and close the top of the bun. Place the assembled bun, pleated side down, onto a pre-cut parchment sheet or a lined steamer. Cover it while you repeat the same process with the remaining dough and filling.
   
2. Rest the buns in room temperature for about 30 minutes before steaming. The bun should rise to at least 1.5-2 times its original size.