Bubble & squeak with sausages & onion gravy

INGREDIENTS

• 750 g floury potatoes, peeled and cut into chunks
• 600 g mixed winter vegetables (see the introduction),, peeled or trimmed and chopped into equal-sized chunks
• olive oil
• 2 knobs of butter
• 1 x 200 g vacuum pack of chestnuts
• 6 good-quality pork sausages,, linked together
• 6 good-quality venison or beef sausages,, linked together
• sea salt
• freshly ground black pepper
• 1 small bunch of rosemary,, leaves picked and finely chopped
• nutmeg,, for grating
• 3 red onions,, peeled and finely sliced
• a few bay leaves
• 1 tablespoon flour
• 125 ml balsamic vinegar
• 300 ml organic vegetable or chicken stock