Pre heat a grill to moderate heat.

Lay the sausages onto a grill pan and gently grill for 15 minutes, turning regularly so they cook evenly and thoroughly and are golden brown.

For the Gravy

Heat the oil in a large pan over a gentle heat. Add the sliced onion and fry gently for about 10 minutes until soft. Add the sugar and balsamic vinegar and stir. Cover with a lid, reduce the temperature and simmer for a further 5 minutes, add the stock and continue to simmer for 10 minutes.

Mix the cornflour with a little cold water to a thin paste and whisk into the gravy, continue to cook for 10 minutes or until the gravy has thickened. Keep warm.

For the Mash

Meanwhile,place the prepared potatoes into a large pan of lightly salted water and bring to a boil, reduce the temperature and simmer until tender, drain the water and return the lid, allow the potatoes to steam until fluffy. Meanwhile pour the milk into a small saucepan, add cubes of butter and bring to a boil, then tip into the steamed potatoes and mash, season with salt and pepper.

To Serve

Pile mashed potato onto warm plates, arrange the sausages on top, drizzle with onion gravy and serve with garden peas.