Preheat the oven to 220°C.
Using a pestle & mortar, crush the fennel seeds, then mix with the mustard and olive oil.
If the pork skin is not already scored, make a few long cuts through it, not touching the meat.
Pat-dry the pork, then rub it with the mustard paste and place it in a roasting dish, skin facing upwards.
Add the garlic cloves (lightly smashed), and the onion (cut in half) to the pan.
Put the dish in the oven for 15 minutes, then take it out and pour in the stock. Cover with foil.
Turn down the heat to 170C and roast the pork in the middle of the oven for an hour. Add the beans for the last 10 minutes of roasting.
Take off the foil, then turn the oven to the grill setting and brown the skin until crispy.
Rest the pork for 5 minutes, before carving, then serve with the beans, crackling and cooking jus.