Night before: pat the belly very dry, sit it uncovered in the fridge skin-up. This is the single step that guarantees crackling.
Bring to room temperature for 45 minutes. Score the skin if it's not already scored. Rub the flesh side with fennel, sliced garlic and pepper. Oil the skin and salt it hard.
Build a bed of onion, halved garlic head, herbs, wine and stock in a deep roasting tray. Sit the belly on top, skin up.
Oven to 160°C fan. Roast for 2.5 hours.
Crank the oven to 230 to 250°C fan. Roast 20 to 30 minutes, watching the skin for full crackle.
Meanwhile, simmer the apples with butter, water and salt for 12 minutes until soft. Mash, finish with lemon.
Rest the belly 15 minutes under loose foil, not touching the skin.
Reduce the pan juices over high heat for 5 minutes to make a gravy.
Carve thick slices. Serve with the crackling shards, apple sauce and pan juices.