Sift flour and baking powder into a bowl, sit in sugar and rub in lard with fingertips untill evenly distributed. Add water and vinegar mixed together and knead to a fairly soft dough. Shape into a smooth ball and rest dough for 30 minutes.
To make buns, divide dough into 6 or 8 portions and mould each into a smooth ball. Roll out on a very lightly floured board to a circle 10cm across. Put a heaped teaspoonful of filling in the centre of the circle and gather the edges together, folding and pleating to make a neat join. Twist dough to seal. Put each bun, join downwards, on a square of greaseproof paper lightly brushed with sesamie oil. Put in steamer, cover and staem for 20 minutes. Serve warm. The cooked buns can be refrigerated overnight and reheated by steaming for 3 minutes before serving.