Blacken onions in a hot pan, add to a large pot with 5 litres of water and other broth ingredients, and simmer for 3 hours.
Ladle the broth through a fine sieve into a container and cool.
Salt the pork belly for 1 hour, rinse, and place in a saucepan with spices, molasses, soy, and 2 litres of broth.
Submerge the pork with a weight and simmer for about 2 hours until tender.
Preheat your oven to 220°C.
Remove the pork from the stock and extract any bones or sinew.
Score the skin, place on greaseproof paper, and roast for 20 minutes.
Reduce the remaining cooking stock in a pan until it reaches a syrupy consistency.
Whisk vinegars, olive oil, and caster sugar together for the dressing.
Toast fennel seeds and thinly slice the cabbage, fennel, onion, and herbs for the slaw.
Toss the slaw ingredients together and dress 20 minutes before serving.
Serve the roasted pork drizzled with the reduced glaze and a side of slaw.