In a mixing bowl, combine milk, yeast, sugar, flour, and oil. Mix on low speed for 5 minutes, then medium speed for 5 more minutes until smooth and elastic.

Remove air bubbles by rolling the dough into a log shape and folding it over itself, repeating three times.

Divide the dough into 10 equal portions, shape each into a smooth bun ensuring no cracks on the surface.

Mix eggs, milk, flour, and butter in a separate bowl until smooth; this creamy blend should be thick yet pourable.

Place a small ball of custard in each dough disc, fold the edges over and pinch to seal securely.

Cover assembled buns with a towel and let rest for 30 minutes in a warm place.

Bring water to a boil and steam the buns for about 10 minutes until fluffy and firm.