How to make it
Dissolve yeast in lukewarm water. Add 1 cup of flour. Mix thoroughly. Cover with a cloth and allow to rise for 1 hr, until bubbles appear. Dissolve ¼ cup sugar and vegetable oil in ½ cup boiling water. Stir well. Cool until lukewarm. Pour into yeast mixture. Add remaining flour.
Knead dough on a lightly floured board until smooth. Put into an extra large, greased bowl in a warm place. Cover with a damp cloth and allow to rise until doubled in size (approx 2 hrs).
Heat 2 tbsp oil in wok. Stir fry finely chopped spring onion and garlic for 30 secs. Add pork cut into small cubes. Stir fry for 1 min. Add soy sauce, oyster sauce, char siu sauce and remaining sugar.
Add dissolved cornflour. Stir fry quickly until pork is glazed. Remove to bowl and allow to cool. On a floured board, knead dough for 1 min and roll into one long, sausage-like roll 5cm in diameter. Slice the roll crosswise into 3cm pieces.
Flatten each piece with the palm of your hand and roll with rolling pin into 8cm rounds. Place 2 tbsp of filling in the centre of each round of dough. Place 2 tbsp of filling in the centre of each round of dough.
Place each Chinese bun on 5cm square baking paper on a steamer tray. Cover with a towel. Allow to rise for 1 hr, until dough springs back when touched with finger. Remove towel. Steam over briskly boiling water for 10 mins.