1. Take the rib out of the refrigerator a couple of hours before you intend to cook it and season it well with sea salt. Let it come up to room temperature.
2. Preheat the oven to 75C fan-forced (95C conventional),or as low as it will go.
3. Rub the rib with extra virgin olive oil and put in a large roasting tin. Place in oven and turn the tin every 30 minutes or so.
4. About 1½ hours into the roasting,slide a meat thermometer into the centre of the beef to check the core cooking temperature. Continue to cook until the reading is 53°C,then remove from oven. (This will take a total of 3-4 hours,depending on your oven. If your oven is a little hotter,you will need to take the meat out a degree or two earlier.)
5. For the horseradish cream,whip the pure cream into soft peaks and fold it gently through the mayonnaise,then fold through the fresh horseradish. Finish with a good grind of black pepper.
6. To serve,place the rib on a chopping board and cut the meat off the bone into 4 even,round slices,then cut the ribs and give them to those who love to chew on the bone. Place the meat slices on four hot plates,thenplace some gratin (recipe below) next to the beef. Serve the horseradish cream on the side and drizzle with extra virgin olive oil and a sprinkle of sea salt.
Neil Perry's potato gratin recipe
Serving suggetsion:Add a side of boiled green vegetables and lashings of sea salt,lemon juice and extra virgin olive oil.