In a mixing bowl, whisk the eggs until completely mixed. Add melted butter and warm milk and whisk until combined.
In another bowl, mix flour, ¼ cup sugar, milk powder. Slowly add the egg mixture into the bowl stirring to mix until it is smooth with no lumps.
Sieve the custard mixture into a pot over low heat. Stir continuously for 10-15 minutes as the mixture thickens until it is solidified enough to separate from the pot surface. Transfer it into a container, cover with cling wrap to exclude air and cover the container with a lid. Refrigerate for 3 hours or overnight.
In a mixing bowl, make the wrapper by combining glutinous rice flour, rice flour, wheat starch, 3 tbsp sugar, ½ cup milk, condensed milk, oil. Mix until it becomes smooth with no lumps.
Cover bowl with a plate and microwave three times: 1 ½ minutes, 1 minute and 30 seconds. Each time carefully take it out and mix with a spoon before putting it back into the microwave. After the third time, let it cool for 15 minutes.
With gloves, knead the dough by hand for 5-10 minutes until texture becomes silky/smooth and not sticky. Divide the dough into 12 portions and roll them into balls. Each ball should weigh about 20 grams.
Take the egg custard out of the fridge and divide into 12 portions and roll them into balls. Each ball should be about 30 grams.
Put each wrapper ball between 2 parchment paper and roll it into a circular shape about 4 inches diameter. Put one custard ball in the middle and wrap it, pinching the edges closed and rolling it into a ball. Repeat for all 12 balls.
In a pan, cook 2 tbsp of glutinous rice flour for 5-10 minutes. For each moon cake ball, coat it with the cooked flour and put it into the mold for 50g moon cake and press for 10 seconds.