1. Dissolve yeast in lukewarm water. Add 1 cup of flour. Mix thoroughly. Cover with a cloth and allow to rise for 1 hour, until bubbles appear.
2. Dissolve ¼ cup sugar and vegetable oil in ½ cup boiling water. Stir well. Cool until lukewarm. Pour into yeast mixture. Add remaining flour.
3. 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 hours).
4. Heat 2 tbsp oil in wok. Stir fry finely chopped spring onion and garlic for 30 secs. Add cooked pork cubes and stir fry for 1 min. Add soy sauce, oyster sauce, Chinese BBQ Marinade and remaining sugar.
5. Add dissolved cornstarch. Stir fry quickly until pork is glazed. Allow to cool in a bowl.
6. On a floured board, knead dough for 1 min and roll into one long, sausage-like roll 5 cm in diameter. Slice the roll crosswise into 3 cm pieces.
7. Flatten each piece with the palm of your hand and roll with rolling pin into 8 cm rounds.
8. Place 2 tbsp of cooled filling in the center of each round. Gather the dough up around the filling by pleating along the edges. Bring the pleats up and twist securely and firmly.
9. Place each Chinese bun on 5 cm square baking paper on a steamer tray. Cover with a towel. Allow to rise for 1 hour, until dough springs back when touched with finger. Remove towel.
10. Steam over briskly boiling water for 10 minutes.