Preheat the oven to 400°F (200°C).
Heat the beef dripping in a pan and add in the onion. Cook over a medium heat stirring occasionally for around 20-30 minutes until soft and dark brown in colour.
In the meantime, place the sausages onto a baking sheet and place in the oven for 25-30 minutes until cooked through and golden.
If making mashed potatoes, place your potatoes on to boil at this stage.
Once the onions have browned and softened, add in the flour and butter and cook for a few minutes then add in the beef stock, mustard and Worcestershire sauce.
Simmer for around 10-15 minutes until thickened.
Drain the potatoes and mash with warm cream and butter. Season with salt and pepper.
To serve, place the mashed potatoes in the centre of the plate, top with a sausage round and pour over the onion gravy.