Pork loin with a great herby stuffing

INGREDIENTS

• ½ higher-welfare pork loin, preferably the rib end, off the bone
• 1 small handful fresh rosemary, leaves picked
• 3 heaped tablespoons fennel seeds
• sea salt
• freshly ground black pepper
• 500 g sourdough or rustic bread
• 2 red onions, peeled and finely sliced
• 3 cloves garlic, peeled and finely sliced
• 1 small handful fresh sage leaves, ripped up
• 1 handful pine nuts
• extra virgin olive oil
• 4 tablespoons balsamic vinegar