Make sure the beef is at room temperature before cooking.

Preheat the oven to 240C and rub the mustard powder and salt and pepper all over the beef fat.

Put the beef into the oven at 240C for 20 mins to sear it.

Turn the oven down to 160C and cook for a further 12 mins per 500g for rare meat, 15 mins per 500g for medium and 20 mins per 500g for well done meat.

Remove from the oven, cover and rest for 20mins

Carve and serve with all the trimmings.