• Preheat oven to 275F. Wrap the pork belly in heavy tin foil (or use 2 layers). Place on baking sheet and roast for 2 hours. Remove from oven and let cool before refrigerating at least 2 hour or up to 2 days.
• Unwrap the pork belly, and slice into 1/2" pieces
• In a large bowl, whisk together the brown sugar, rice vinegar, fish sauce, soy sauce and water.
• Heat a wok or large saute pan over high heat. When hot, swirl in cooking oil and add several slices to the wok, but do not overlap. Fry each side until browned. Remove to plate. Repeat with remaining.
• Turn the heat to medium-low. Add in the garlic, ginger, chiles (if using) and green onion. Saute for 30 seconds until fragrant. Pour in the remaining caramel sauce into the pan.Return the pork belly slices back into the wok and let simmer for 10 minutes.

FOR THE BUNS

• Follow the directions on the package to make the dough, cover and let rise for 20 minutes.
• Sprinkle clean work surface with the all-purpose flour. Place the dough on work surface and cut into 16 equal pieces. Roll each piece into a ball and keep all balls loosely covered with plastic wrap or towel. You'll work with 1 ball at a time, keeping the rest covered.
• Use a rolling pin to roll out each ball into an oval, about 4"x3". Fold the oval in half to create bun shaped. Place on parchment square. Keep covered loosely with plastic wrap or towel to prevent drying out. Repeat with remaining dough.
• Prepare steamer (see photos above). Steam the buns for 15 minutes. You'll have to steam in 2 or 3 batches (avoid overcrowding the buns).

FOR THE CHILI SAUCE

• Place the green onion, chili, vinegar and salt in a small heatproof bowl. In a small saucepan, heat the cooking oil until smoking, remove from heat and immediately pour on top of the green onion mixture. Please be careful, the oil will bubble and crackle.
• To serve, carefully open each bun, spread a bit of hoisin sauce in the bun. Add a slice of pork belly and top with the chili sauce. Add a bit of kimchi if desired.