Place the potatoes in a pot and fill with cold water until just about covered. Add in 2 tsp salt and bring to a boil until the potatoes are knife tender (10-15mins depending on size). Drain, then leave to sit in the colander for 5mins to allow steam to escape.

Add the potatoes back to the pot alongside 4 tbsp butter. Mash until relatively smooth, then stir in cream, mustard and a generous amount of salt & pepper (to taste). Mash a little more if needed.

Meanwhile, at the same time, add the sausages to a large pan over medium heat in a drizzle of oil. Turn frequently until deep golden and lightly charred with the centre piping hot. Keep the heat at a medium to render down the fat and cook the sausages through evenly. This can take 15mins or so depending on the size of the sausages.

Remove the sausages and leave the fat behind. There should be around 1 tbsp fat left. If there's more, reduce the butter (you want 3 tbsp fat between the sausage fat & butter). Melt the butter in the pan, then add in the onion and fry until soft and golden. Stir in 3 tbsp flour until a paste forms, then gradually pour in the beef stock, stirring as you go to prevent lumps forming.

Stir in Oxo, Worcestershire sauce, black pepper and salt if desired. Simmer to further thicken if needed. If it over-thickens, just add a dash more stock or water to thin it out.

Serve sausages on top of mash with gravy poured over!