Pat beef dry with paper towels, sprinkle with salt and pepper all over. Place the beef on a rack on a tray then refrigerate uncovered 12 to 24 hours.

Mix Butter Slather ingredients in a bowl.

Remove the beef from the fridge 2 hours prior to cooking.

Heat oil in an ovenproof heavy based pan over high heat until smoking. Brown the surface of the beef all over.

Put the beef back on the rack to cool for 15 minutes.

Preheat oven to 120°C/250°F.

Put beef back in cooled skillet. Slather ¾ of the butter onto the beef – top and sides.

Roast for 15 minutes. Remove, slather remaining butter onto the top and sides. Roast for a further 25 – 35 minutes or until the internal temperature is 53°C/127°F for medium rare.

Remove beef from the skillet onto a cutting board and rest for 10 minutes.

Pour all juices in skillet into a bowl or jug and reserve.

Turn the stove onto high, add mushrooms and cook until they start to sweat.

Add thyme and garlic, and cook for a further 2 minutes until the mushrooms are softened.

Add chicken stock/broth and reduce by half. Add marsala, cream, pepper and remaining reserved roasting juices. Simmer on medium / medium high for 5 minutes until it reduces by half and the sauce is thickened.