XO Soused - har gau dumpling

What is har gau [蝦餃] ? What starches make up its sticky texture and clear skin? What techniques are required to create the unique, juicy ‘bounce’ of its prawn filling? How important is a vigorous steam? How far back in Chinese history did the required flours make their appearance? How far did Cantonese millionaires of 19th century South China push local dim sum chefs to create the modern har gau that we know and love today, and are these so different from early har gau of the Song dynasty - nearly 1,000 years ago?