Pound the garlic, bay, pepper, 1 tsp sea salt and 1 tbsp of the fennel seeds using a pestle and mortar, then stir in 1 tbsp oil. Place the pork, skin-side up, in a clean sink and pour over a kettleful of boiling water (this tightens the skin – the first step towards great crackling). Drain, pat dry and place, skin-side down, on a chopping board. Rub the garlicky paste all over it, then roll up the loin and tie it at intervals with kitchen string. Arrange the onion and lemon in the centre of a roasting tin and sit the pork on top, skin-side up. Rub the rind with the remaining salt and leave at room temperature, uncovered, for 1 hr.