Melt the butter in a saucepan over a medium heat, add the onion and fry gently for 8-10 minutes, or until softened.
Stir in the remaining stuffing ingredients, except for the vegetable oil, until well combined. Season, to taste, with salt and freshly ground black pepper.
Using wet hands, shape the sausage meat mixture into 16 equally-sized balls. Place on a lightly greased baking tray, cover with cling film and chill in the fridge for at least 30 minutes.
Preheat the oven to 200C/180C Fan/Gas 6.
Heat the oil in a large frying pan over a high heat. Add the stuffing balls and fry for 4-5 minutes, turning once during cooking, until golden-brown on both sides.
Return the fried stuffing balls to the baking tray (or, if there is room, place them into the same roasting tray as the turkey or chicken). Cook the stuffing balls in the oven for 20-25 minutes, or until cooked through. If they brown too quickly during cooking, cover with aluminium foil.
Serve with roast turkey, roast chicken, or other roast meat.