Boil the chopped potatoes in salted water until tender, about 15 minutes.
In a skillet, cook the sausages for about 10-12 minutes, turning until browned.
Add sliced onions to the skillet and sauté until golden brown.
Drain the potatoes and return them to the pot.
Add butter and milk to the potatoes, and mash until smooth.
Season the mashed potatoes with salt and pepper.
Heat the gravy in a separate saucepan until warmed through.
To serve, place a scoop of mashed potatoes on a plate.
Top with sausages and pour over the gravy.
Garnish with fresh parsley before serving.