Heat oven to 160°C.Heat the oil in a flameproof casserole dish over a medium-high heat. In batches, brown the pork belly well, then transfer to a plate. Tip the sugar into the dish and cook over a medium heat until starting to dissolve and caramelise, then quickly stir in the garlic, ginger and star anise, and cook for 1 min.
Carefully pour in the rice wine and soy sauce – watch out, it will spatter – and simmer to dissolve the sugar. Stir the pork into the caramel to coat, then add 100ml water and the five-spice, and bring to a simmer. Put the lid on and cook in the oven for 1 hr 30 mins.
Remove from the oven, uncover, put on a high heat to simmer and reduce the sauce until sticky. Can be prepared up to 2 days ahead and chilled. Reheat with a splash of water.
To create the extra spicy hoisin sauce (if desired) – in a small saucepan, mix the hoisin sauce and Sriracha sauce together. Heat gently over a medium heat until it has warmed through.
Steam bao buns for 10-12 minutes, just before serving.
Once ready, prepare everything for serving – split open freshly steamed bao buns.
Spread both sides of the bun with the sauce (if desired).
Layer pieces of pork and vegetables inside.
Serve and enjoy.