To make the spice mix, toast the star anise and peppercorns in a frying pan until fragrant, then grind to a powder with 1 tbsp flaky sea salt using a pestle and mortar. Tip into a bowl and mix through the zest, bay leaves, stock cube and breadcrumbs, then set aside.
Lay the belly skin-side down on a board with a longer edge facing you, and cut 8-10 deep slashes in the flesh. Massage the spice mix into the flesh, getting deep into the cuts. Roll the belly tightly to form a roulade-style joint, then tie evenly with butchers’ string. Set aside until ready to cook. Can be prepared up to one day ahead and chilled.
Heat the oven to 240C/220C fan/gas 9. Lay the pork on a shallow roasting tray, rub the oil over the skin and season with salt. Roast for 20 mins, then turn the oven down to 180C/160C fan/gas 6 and roast for another 1 hr 40 mins, basting with the fat in the pan a few times. If the crackling hasn’t crackled by this point, turn the oven back up to 240C/220C fan/gas 9 and check every few minutes until crackled. Rest for 30 mins, then use a serrated knife to carve into thick slices.