XO Soused - Char Siu bun

What is Char Siu? Directly translated at ‘fork roasted’ what are the origins of this technique in China, and what are the connections to Central Asian roasting techniques? What other ingredients are stuffed with the barbequed neck-end of pork into the fluffy bun? What are the techniques and ingredients to create that texture and finish to the bun itself? How did China develop leavening agents and leavened dough and what is the historical connection with wine production?