Wrap 8 large sage leaves around the centre of each sausage and secure with a cocktail stick if required. Chop the remaining sage.
Place the onions, garlic and half the chopped sage in a roasting tin and toss in 1 tablespoon oil.
Roast in the preheated oven for 20 minutes until the onions are tender.
Meanwhile, heat the remaining oil and fry the sausages for 5 to 6 minutes until evenly browned and add to the roasting tin for the last 15 minutes.
Remove from the oven then set the sausages aside and keep warm. Transfer the onions to a small saucepan then add the vinegar and sugar and cook for 5 minutes until caramelised. Stir in the remaining sage and season. Serve the onion chutney with the sausages.