Mix cornstarch with water and set aside for couple of minutes until well combined.

In a small sauce pot, add starch water, oyster sauce, hoisin sauce, light soy sauce, sugar and heat over slowest fire until there are big bubbles. Then mix with the char siu dices.

Cover the filling and place in fridge for 30 minutes.

In a stand mixer, place all of the dough ingredients in and then knead for 7-9 minutes at slow speed. Then cover and rest for 10 to 15 minutes.

Slightly re-knead the dough for another 2 minutes until the smooth becomes very smooth. Shape into long log first and then divide the dough into 12 equal portions. Re-knead each wrapper dough until the surface becomes smooth.

Roll each of the wrapper dough into a round wrapper around 10 cm in diameter with thin edges. Scoop around 1 tablespoon of filling in the center and seal the buns completely. Repeat to finish all of the buns.

Place the buns on baking papers and then place in steamer. Cover the lid and rest for another 20 minutes at a room temperature around 28 degree C to 30 degree C. In cold water days, heat water in a pot for several minutes until warm but not boiling and then place the steamer on the warm water, rest for 15 to 20 minutes.

Start the fire and steam the buns for another 20 minutes, turn off fire and stand for 5 minutes before enjoying.

Re-steam the buns if they are cooled. No changes for the taste.