Balsamic-Baked Onions and Potatoes with Roast Pork

INGREDIENTS

• 1 medium red onion, peeled and quartered
• 2 wine glasses white wine
• 6 cloves garlic, crushed
• 1 1/2 cups cheap balsamic vinegar
• 2 tablespoons freshly ground fennel seeds
• Sea salt and freshly ground black pepper
• 2 stalks celery, trimmed and chopped
• 4 bay leaves
• 3 1/2 pounds medium-sized waxy potatoes (all purpose), peeled and quartered lengthwise
• 1 whole bulb garlic, quartered or smashed
• 1 (3 1/2-pound) boneless rolled pork loin, preferably free-range or organic, skin off, fat scored in a crisscross pattern
• Salt and pepper
• 5 medium red onions, peeled and quartered
• Olive oil
• 7 ounces butter, cubed
• 1 bunch fresh rosemary, leaves picked and chopped
• 1 small bunch fresh rosemary, leaves picked and finely chopped