Combine (A) and stir till sugar dissolves. For ingredients (B), break up the yeast and drop it into the lukewarm water. Leave aside to stand for 10 minutes until yeast bubbles and turns frothy.
Sift Hong Kong flour and baking powder, and combine them with the salt in a large mixing bowl.
Make a well in the centre; pour in frothy yeast, sugar mixture and egg. Combine well and mix to form a dough.
Remove dough onto floured tabletop. Knead dough until smooth (about 10 minutes by hand). Place dough in mixing bowl; cover with a damp tea towel and leave to rise for one to one and a half hours or until double in volume.
(It depends on the weather. On a hot day it may be faster but on a cool day it may take a longer time.)
Turn the dough out onto a floured working surface and knead lightly to expel any large air bubbles. Divide the dough into two equal portions and form each one into a rectangular piece (30cm x 13cm).
Brush the surface with the lard separator or corn oil; sprinkle very lightly with flour. Roll up carefully, Swiss roll-style. Cut with a sharp knife into 2.5cm-thick pieces.
Place two pieces together, one on top of the other; using a chopstick or satay stick dipped in flour, press the centre to join both ends together.
Put flower bun on a piece of cut-out grease-proof paper. Arrange buns in a steaming tray. (Do not put them too near to one another as they need space to expand.) Steam over rapidly boiling water for 10 to 12 minutes.